**Analysis of Network Structure of Urban Bike-Sharing System: A Case Study Based on Real-Time Data of a Public Bicycle System**

#### **Yi Yao 1 , Yifang Zhang 1,\*, Lixin Tian 1 , Nianxing Zhou 2 , Zhilin Li 3 and Minggang Wang 1,4**

Received: 12 July 2019; Accepted: 27 September 2019; Published: 30 September 2019

**Abstract:** To better understand the characteristics of a bike-sharing system, we applied complex network methods to analyze the relationship between stations within the bike-sharing system. Firstly, using Gephi software, we constructed the public bicycle networks of different urban areas based on the real-time data of the Nanjing public bicycle system. Secondly, we analyzed and compared degree, strength, radiation distance, and community structure of the networks to understand the internal relations of the public bicycle system. The results showed that there were many stations with low usage of public bicycles. Furthermore, there was a geographical division between high-demand and low-demand areas for public bicycles. The usage of public bicycles at a station was not only related to land use but also related to the usage of bicycles at stations nearby. Moreover, the average service coverage of the public bicycle system was consistent with the original intention of "the first and last mile", and public bicycles could meet different travel needs.

**Keywords:** sustainable mode of transportation; bike-sharing system; public bicycle; complex network; network structure

#### **1. Introduction**

Bike-sharing systems (BSSs) not only facilitate people with the trouble of "the first and last mile" but also provide them with a sustainable and carbon-free mode of transportation. In 1965, an NGO called Provo established a public bicycle system (PBS) to reduce air pollution and relieve traffic congestion in Amsterdam, which is regarded as the prototype of BSSs [1].

With economic booming and social modernization, bicycles are not the top choice in most countries. Nevertheless, due to increasingly serious air pollution and traffic congestion, public bicycle, a station-based bike-sharing, has gradually become a significant transportation alternative once again. However, untimely rebalancing operations and unreasonable station distributions not only reduce users' satisfaction but also increase the scheduling and maintenance costs, which results in waste of public resources. Therefore, studies on PBSs are beneficial to solve the issue of "unavailable bicycles and unavailable docks" and can improve the social and economic benefits of PBSs.

Scholars have carried out a lot of research on BSSs and achieved fruitful results. Characteristics of users and stations, influencing factors, and built environment are all main research contents. Users' gender [2–7], age [3,6–8], income and education [2,5,6,9,10], weather conditions [11–13], infrastructure construction, population density, built environment [7,12–19], and relationship with other means of transportation [20–33] have been confirmed to affect the usage of bike-sharing. On the other hand,

in order to solve the problem of rebalancing, optimization of BSSs has also become another hot issue [34–43]. As far as research methods are concerned, statistical methods such as correlation analysis, clustering analysis, and regression analysis are adopted to analyze characteristics and influencing factors [3,7,9,13,14,19,20,22,23,44], and optimization algorithms are used to solve rebalancing operations for BSSs [35,38–40,42,43].

The existing researches mainly discuss BSSs from the aspects of the relationship between BSSs and external environments, while studies from the perspective of the relationship between internal stations of BSSs are insufficient. To fill this gap, we built public bicycle networks (PBNs) using Gephi software according to complex network methods, aiming to analyze internal correlation characteristics of BSSs.

The remainder of the paper is organized as follows. Section 2 reviews the relevant literature. Section 3 provides the data and methodology, and Section 4 analyzes the results. Lastly, Section 5 presents conclusions.

#### **2. Literature Review**

#### *2.1. Relationship between BSSs and External Environments*

Relationship between BSSs and external environments is a hot issue.

Weather conditions are an important influencing factor for the use of public bicycles. More bicycles were used in good weather, while rain, snow, low temperature, and gales resulted in less use [11–13].

Infrastructure construction and population also profoundly influence the use of bike-sharing. In Montreal, increasing the number of stations played a more active role in cycling than increasing the number of parking piles [12]. More public bicycle lanes promoted the use of public bicycles [14]. In general, station capacity, zonal population, employment density, commercial land, and daily life places nearby were positively correlated with cycling [7,13,15–19].

The relationship between BSSs and other transportation systems is getting more and more attention. Scholars analyzed the impact of bike-sharing on walking, cars, public transportation, and subways. Many results showed that bike-sharing replaced walking and public transportation to some extent, and bike-sharing was expected to play a more important role in reducing car use [2,20,21,25–29]. Subway stations were important starting and ending stations of BSSs, and the increase of cycling flow would lead to an increase of average daily subway flow [21,23,32]. Some researchers found that sudden change in public transport services, such as a public transit disruption or a strike, would affect the use of bicycles significantly [30,31]. As for free-floating BSSs and station-based BSSs, Li et al. pointed out that the former had a greater effect on the latter especially on weekdays and on young people [24]. Luo et al. found that greenhouse gas emissions factor of free-floating BSSs was 82% higher than station-based BSSs based on life cycle assessment [33].

#### *2.2. Internal Relationship of BSSs*

Some studies of BSSs carried out clustering analysis on the stations, which essentially explored the relationship between the stations and also the internal relationship of the systems. The usage pattern of stations was identified by the clustering method, and the clustering results were influenced by station locations and socioeconomic situations [7,23,45–47]. More bike-sharing movements were observed within a cluster than between clusters in Lyon [48]. However, clustering analysis mainly distinguishes the similarity of stations and does not highlight the relationship between them.

Recently, some scholars have begun to focus on BSSs using network analysis methods. Rixey pointed out that station network effects were extremely important to ridership levels, with a robust, statistically significant relationship within systems. Station network variables were put forward to test the effects of public bicycle station network density, distribution, and size on cycling. The results revealed that there was a positive correlation between the number of stations within 4800 m of a given station and the number of people cycling monthly [9]. Saberi et al. combined geospatial methods with complex network methods to better understand the interdependence between BSSs and public

transportation systems in London [31]. Austwick et al. explored BSSs in different cities by network analysis, and they found that the strength rank curve for the top 50 stations in each system displayed a similar scaling law. Furthermore, community detection in the network could identify local use [49]. Lin et al. proposed a novel graph convolutional neural network with data-driven graph filter model to predict station-level hourly demand with fairly good prediction accuracy. Graph network analysis showed that this model could not only gather more information from more stations but also utilize more underlying correlations between stations [50].

Although the existing research has provided us a lot of insights, there is potential to deepen the knowledge of BSSs. (1) The relationship between BSSs and external environment has been more in-depth, while the internal correlation of BSSs needs to be expanded. Complex network analysis is applied to study the internal correlation between nodes according to their connection relationship, which is relatively under-utilized to understand BSSs [49]. (2) How to construct a bike-sharing network and select appropriate statistical analysis indicators is an important issue that needs to be discussed. As research on the internal relationship of BSSs by complex network analysis is still inadequate, this problem is the premise of understanding the characteristics of BSSs. (3) How to select representative areas for comparative analysis to gain an in-depth understanding of BSSs is also another problem that we should pay much attention to. Because of different population density, employment density, built environment, and land use in different areas, characteristics of BSSs also vary. That is, conclusions and suggestions put forward according to the information in certain regions are not necessarily applicable to other regions. As a result, regional information should be gathered for system operators to possess a more comprehensive knowledge of BSSs.

According to the spatiotemporal real-time data of the PBS in Nanjing, we first constructed the public bicycle networks (PBNs) of different urban areas with Gephi software. Then, we not only analyzed statistical indicators such as degree and strength but also defined "radiation distance". Finally, we analyzed internal correlation characteristics between stations and compared characteristics in different regions.

#### **3. Data and Methodology**

We chose Nanjing PBS in China as our case study. Nanjing is the center of politics, economy, education, and culture in Eastern China and also the provincial capital of Jiangsu Province, with an area of 6587.02 km2 . At the end of 2016, the total population was 8.27 million with the urban population density 1484 people/km2 . There were 10,402 public transport vehicles in operation, with a network of 10,476.3 km in length and a total of 1776 million passengers, ranked 6th in China in 2016. Behind the economic prosperity and the development of modern transportation, air pollution cannot be ignored. In 2016, the annual average concentration of pm10 was 0.085 mg/m3 , with exhaust emissions of 773.482 billion m3 and soot emissions of 48,600 tons [51]. Therefore, the study of Nanjing PBS is of positive significance to improve the efficiency of PBSs in modern metropolis with high population density, heavy traffic, and air pollution.

Nanjing PBS has more than 600 stations almost covering the main city since Nanjing Public Bicycle Company was founded in 2015. People pay a deposit for a public bicycle card. The charge is zero for the first two hours, one Chinese yuan for the third hour, and three Chinese yuan per hour for the fourth hour and above. A user picks up a bicycle at a station and returns it in the parking pile at the destination station to complete this trip.

#### *3.1. Data*

Nanjing Public Bicycle Company provided us with 662,007 anonymous daily data from 20 March 2016 to 26 March 2016, including user ID, renting (returning) stations, renting (returning) time, longitude and latitude of returning stations (see Table 1). Some situations such as bicycle and timer malfunctions would lead to inaccurate cycling time records. Thus, the data that indicated less than 2 min or more than 2 h usage were excluded, and the number of actual valid data was 593,582. In this week, 131,695 users used public bicycles, with an average of 4.5 times, the average duration of 15.77 min, and the average cycling distance of 1.43 km, which was consistent with "the first and last mile".

**Table 1.** Sample data of Nanjing public bicycle system (PBS).

Gulou District is the central area and also the political, economic, educational, and cultural center of Nanjing. The resident population of Gulou District is 1,249,400, ranked 1st in the six main urban districts of Nanjing, and the area is 53 km2 , with a population density of 23,574 people/km2 . In 2016, the total production value of Gulou District was 112.303 billion Chinese yuan, ranked 1st, and the per capita annual disposable income was 54,791 Chinese yuan. High population density and employment density lead to high demand for public bicycles. Qixia District is located in a remote area with a large area and low population density. The resident population of Qixia District is 693,300, ranked 3rd, and the area is 395.44 km2 , with a population density of 1753 people/ km2 . In 2016, the total production value of Qixia District was 92.723 billion Chinese yuan, ranked 2nd, and the per capita annual disposable income was 48,379 Chinese yuan. Low population density may be the main reason for low demand for public bicycles. Gulou District and Qixia District, one as the center of economics and politics and the other as the emerging district of culture and education, are different in geographical location, regional functions, distribution of stations, and demand for public bicycles. Therefore, it is reasonable to select these two districts to analyze and compare the internal correlation characteristics of PBNs.

#### *3.2. Complex Network Theory*

Complex network theory explores topological structures and properties of a network utilizing graph theory and statistical physics, which can show the nature of the network without depending on the specific location of nodes and specific shape of edges. In a network, nodes represent research objects, and edges connecting two nodes represent their relationship. Now, complex network theory has been successfully applied in financial markets [52–54], transportation systems [9,31,49,50,55–57], and energy fields [58–61].

We treat a station as a node. If a user rents a public bicycle at station A and returns it to station B, there is a directed edge pointing from A to B. The weight of this edge is equal to the number of cycling records from A to B, which can show how close the relationship between A and B is. Hence, a PBN is a directed weighted network.

#### 3.2.1. Degree

For a PBN, public bicycles rented from station *i* are returned to various destination stations, and the number of these destination stations is defined as the out-degree *k out i* of node *i*. Public bicycles rented from various origin stations are returned to station *i*, and the number of these origin stations is defined as the in-degree *k in i* of node *i*. The calculation formulas of *k out i* and *k in i* are as follows:

$$k\_i^{out} = \sum\_{j=1}^{N} a\_{ij\prime} \qquad k\_i^{in} = \sum\_{j=1}^{N} a\_{ji} \tag{1}$$

where *aij* denotes an element of adjacency matrix, that is, if there is a directed edge from station *i* to station *j*, *aij* = 1; otherwise, *aij* = 0. *N* represents the number of nodes.

#### 3.2.2. Strength

For a PBN, the out-strength *s out i* represents the number of public bicycles rented from station *i,* and the in-strength *s in i* represents the number of public bicycles returned to station *i.* The calculation formulas of *s out i* and *s in i* are as follows:

$$s\_i^{out} = \sum\_{j=1}^{N} w\_{ij\prime} \qquad s\_i^{in} = \sum\_{j=1}^{N} w\_{ji} \tag{2}$$

where *wij* represents the weight of the edge from station *i* to station *j.*

#### 3.2.3. Radiation Distance

Compared with general complex networks, PBNs have their own way of calculating path length. For example, if one user rents a public bicycle from station A and returns it to station B and another user rents one from station B and returns it to station C, there is a path from station A to station C according to the concept of "path" in complex network theory. However, we cannot explain this path as a user starting from station A and going to station C via station B. Furthermore, there may be no records renting one from station A and returning it to station C. Therefore, applying "path length" of complex network theory to PBNs may be of no significance. As a result, we define "radiation distance" to measure the distance between stations (nodes).

In a PBN, we define the radiation distance from station A to station B as the actual distance between them, and the radiation distance of station A is the average radiation distance from station A to the other stations. Hence, the radiation distance of a PBN is the average radiation distance of all the stations.

#### 3.2.4. Community Structure

In a network, nodes in the same community are closely connected. Modularity Q is used to evaluate the quality of community division, and community division with the maximum value of modularity is optimal. For a directed weighted complex network, modularity is calculated as follows:

$$Q = \frac{1}{W} \sum\_{i,j} \left( w\_{ij} - \frac{s\_i^{out} s\_j^{in}}{W} \right) \; \delta(M\_{i\nu} M\_j) \tag{3}$$

where *W* is the sum of all the weights, *Mi* is the community that station *i* belongs to and *Mj* is the community that station *j* belongs to. If station *i* and station *j* belong to the same community, δ(*Mi* , *Mj* ) = 1, otherwise, δ(*Mi* , *Mj* ) = 0.

#### **4. Results**

#### *4.1. The Construction of the PBN*

We first treated each public bicycle station in Gulou District as a node, and then added the stations in other districts that had public bicycle renting or returning with the nodes into the network. Hence, there were totally 587 stations (nodes) in the PBN of Gulou District. There were directed edges between the nodes, and the weights were the number of public bicycles rented or returned.

#### *4.2. The Analysis of Out-Degree and In-Degree*

The average in-degree of the PBN of Gulou District was 57 with the maximum being 287. Since the in-degree of each station was numerically dispersed, we performed interval segmentation to better understand its distribution. We first divided the values of in-degree by the interval length of 20. Then, we considered the integer closest to the weighted average of in-degree and the number of the

−

−

stations within the interval as the representative of the interval value. In this way, we got the in-degree distribution, see Figure 1a. In a log–log plot, the least square estimation was applied to estimate the in-degree distribution, and the regression equation was *y* = −1.2221*x* + 2.3808 with the coefficient of determination *R* 2 = 0.897, which showed a good fitting effect (see Figure 1b). – −

**Figure 1.** (**a**) The in-degree distribution of the public bicycle network (PBN) of Gulou District; (**b**) the in-degree distribution estimation in a log-log plot.

The average out-degree of the PBN of Gulou District was 57 with the maximum being 289. Figure 2a shows the out-degree distribution. In a log–log plot, the regression equation was *y* = −1.1262*x* + 1.9299 with the coefficient of determination *R* 2 = 0.876 (see Figure 2b). As a result, the in-degree and out-degree distribution of the PBN of Gulou District followed the power-law distribution with the power exponents of 1.22 and 1.13, respectively, which were smaller than power exponents of scale-free networks between 2–3. According to the data, there were 245 stations with an in-degree of less than 20, accounting for 41.7% of all the stations, and there were 235 stations with an out-degree of less than 20, accounting for 40.0%. These results indicated that the percentage of the stations with small in-degree or out-degree was lower than that of typical scale-free networks.

**Figure 2.** (**a**) The out-degree distribution of the PBN of Gulou District; (**b**) the out-degree distribution estimation in a log-log plot.

– There were 225 stations (nodes) in the PBN of Qixia District. The average in-degree and out-degree were both 11, and the maximum in-degree and out-degree were 93 and 87, respectively, which were smaller than those of the PBN of Gulou District. Geographically, Gulou District borders Qixia, Xuanwu,

–

Qinhuai, Yuhuatai, and Jianye districts, while Qixia District borders Gulou and Xuanwu districts. From the perspective of station size, there were 175 stations in Gulou District and 41 stations in Qixia District. Therefore, there were big gaps between the two PBNs in station connections and station size.

The in-degree distribution and out-degree distribution of the PBN in Qixia District were similar to long tail distribution (see Figure 3) and they followed the power-law distribution with the power exponents of 1.33 and 1.21, respectively. The power exponents were larger than those of the PBN of Gulou District, which probably meant idle situation of stations in Qixia District was more serious than that in Gulou District.

**Figure 3.** The in-degree and out-degree distribution of the PBN of Qixia District.

#### *4.3. The Analysis of Out-Strength and In-Strength*

Table 2 lists the top ten stations of the PBN of Gulou District based on in-strength and based on out-strength, and the number in brackets after the station name is the station number. Nine of the top ten based on in-strength and the top ten based on out-strength were the same except Longjiang Stadium East Station and Mingcheng Century Park East Gate Station. At the same time, Table 3 lists the bottom ten stations, and the number in brackets after the station name is the station number. The bottom ten based on in-strength and the bottom ten based on out-strength were nearly the same except the "724 Institute" Station and Shengshi Garden Station. This result indicated that renting flow and returning flow at a station was almost equivalent. Moreover, the strength of the top ten was much stronger than that of the bottom ten, which showed that the usage of public bicycles at different stations varied greatly.

Sugu atio ty o bal Servi Figure 4 shows the geographical distribution of these stations. The red and purple marks correspond to the top ten and the bottom ten stations in Tables 2 and 3, respectively. There are 11 different stations in Table 2, so there are 11 top ten stations in Figure 4 without distinguishing in-strength from out-strength, and the same is true for the bottom ten. There were regional differences in the use of public bicycles. The bottom ten stations were mainly distributed in the north of Metro Line 4, while the top ten were in the south. According to the land use, the commercial land, for example, Xinjiekou Huaqiao Road and Fenghuang business area as well as other cultural and recreational facilities, sports facilities, and educational institutions were concentrated in the south of Metro Line 4. The distribution of stations may indicate that areas close to central business districts had a higher demand for public bicycles due to their high population density and employment density, that is, the more social and economic activities, the more use of public bicycles. Hence, adequate and timely supply of public bicycles around these areas is the priority.

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**Table 2.** The top ten stations of the PBN of Gulou District.

**Table 3.** The bottom ten stations of the PBN of Gulou District.

**Figure 4.** The distribution of the top ten and the bottom ten stations of the PBN of Gulou District.

We should point out that many stations with strong strength were close to subway stations, such as Jiaheyuan Station and Jiqingmen Street Subway Station, Yingchunli West Gate Station and

Hanzhongmen Subway Station, Nanjing University of Chinese Medicine South Station and Shanghai Road Subway Station, which indicated that subway stations were important starting and destination stations for cycling. Therefore, the construction of bicycle stations around subway stations is an important measure to promote the usage of public bicycles.

It was worth noting that there was still low usage of public bicycles even in densely populated areas. There were several residential areas around Qingjiang Xiyuan North Gate Station, and Qingjiang Xiyuan West Gate Station was also nearby. According to the records, almost 60% of the stations associated with these two stations were the same. In fact, Qingjiang Xiyuan West Gate Station was closer to the bus stop and subway station, so the usage of public bicycles was higher than that of Qingjiang Xiyuan North Gate Station. Except for station location, competitive relationship with other stations also affected the usage of public bicycles. Therefore, unreasonable station setting not only reduced the efficiency of PBSs but also led to a waste of public resources.

In directed weighted networks, nodes with strong strength are worth studying. We analyzed Qingliangmen Suguo Supermarket Station, which had the strongest in-strength and out-strength of the PBN of Gulou District.

Figure 5 shows the station distribution around Qingliangmen Suguo Supermarket Station. On the one hand, Mochou Lake Subway Station West Station, Lixue Primary School Station, Huayang Jiayuan North Gate Station, and Yingchunli West Gate Station contributed the most to the in-strength of Qingliangmen Suguo Supermarket Station. On the other hand, the most frequent destinations of this station were Mochou Lake Subway Station West Station, Huayang Jiayuan East Gate Station, Lixue Primary School Station, Jinxin Garden North Gate Station, and Suning Qianqiu Garden East Gate Station. The results showed that if an area where supermarkets, residential areas, subway stations, and schools were concentrated, it was always the main area for the use of public bicycles, which was consistent with the existing research results [7]. Furthermore, in-strength and out-strength of the stations around Qingliangmen Suguo Supermarket Station were above the average level of the network. The observed data showed that the usage of public bicycles at a station was not only related to the built environment but also affected by the usage of bicycles at stations nearby. Ensuring the availability of public bicycles and parking piles of these key stations would have a direct impact on the use of public bicycles throughout the whole area.

As a popular supermarket in Gulou District, Qingliangmen Suguo Supermarket is adjacent to 10 residential areas, including Huayang Jiayuan, Jinxin Garden, Yingchunli, and Suning Qianqiu Garden, and many users cycle to and from the communities and the supermarket every day. Table 4 lists the comparison of the distances and time required from these communities to the supermarket by different travel modes. The comparison indicated that public bicycle was a time-saving means of transportation when the distance was about 1000 m. Convenience, speed, and economy are the advantages of public bicycles for short-distance travel.

**Table 4.** Comparison of different travel modes.

The top ten stations of the PBN of Qixia District based on in-strength were also the top ten stations based on out-strength (see Table 5), and the same was true for the bottom ten (see Table 6). Figure 6 shows the distribution of these stations. The red and purple marks correspond to the top ten and the bottom ten in Tables 5 and 6, respectively. Most of the top ten stations were located around Maigaoqiao Subway Station and along Heyan Road, the major economic area in Qixia District. In particular, the in-strength and out-strength of Gate 1 of Maigaoqiao Subway Station were significantly stronger

than the other stations due to the origin station of Metro Line 1. At the same time, six stations within 1200 m around Maigaoqiao Subway Station had strong in-strength and out-strength, forming an area of high demand for public bicycles. Among the six stations, Qiancaomingyuan South Station and Jinghongyuan South Station contributed the most to in-strength and out-strength, which indicated that public bicycle was an effective means of transportation between communities and important transportation hubs. As a result, public bicycles can bring people more convenience if the connection of public bicycle stations with other transportation stations is well projected in areas with sparse distribution of public transportation. In addition, the usage of public bicycles in Qixia District was less than that in Gulou District.

**Figure 5.** The station distribution around Qingliangmen Suguo Supermarket Station. y.

**Figure 6.** The distribution of the top ten and the bottom ten stations of PBN of Qixia District.

**Table 5.** The top ten stations of the PBN of Qixia District.

**Table 6.** The bottom ten stations of the PBN of Qixia District.

The stations with strong or weak strength in the PBNs had a clear division in the distribution. Areas where supermarkets, residential areas, schools, and subway stations were gathered were always areas with high demand for public bicycles. The usage of public bicycles at a station was not only related to the concentration of social and economic activities but also affected by the usage of bicycles at stations nearby.

#### *4.4. The Analysis of Radiation Distance*

The actual distances between stations were calculated based on longitude and latitude of the stations. The average radiation distance of the PBN of Gulou District was 1.59 km, which was consistent with the original intention of "the first and last mile". Because of the dense distribution of public bicycle stations in Gulou District, it was easier to obtain public bicycle services in shorter distances. Furthermore, 11.3% of the cycling distances were more than 3 km, 0.13% were more than 10 km, and the maximum distance was 17 km, which indicated that public bicycles were not only used for short-distance travel but also for long-distance travel because of convenience, economy, and exercise purposes.

The average radiation distance of the PBN of Qixia District was 1.87 km, which was longer than that of Gulou District. According to the records, 15% of the cycling distances were more than 3 km and the proportion at Yanziji Park Station was even more than 30%. In fact, the area of Qixia District was seven times that of Gulou District, and there were fewer stations in Qixia District, which led to more long-distance cycling.

#### *4.5. The Analysis of Community Structure*

According to Louvain algorithm, the PBN of Gulou District was divided into five communities numbered 1 to 5. As explained in network construction, the PBN of Gulou District also contained stations in other districts that had bicycle renting and returning with stations in Gulou District. In order to understand the relationship between public bicycle stations within Gulou District, we removed stations in other districts, only leaving stations in Gulou District (see Figure 7).

**Figure 7.** The community distribution of the PBN of Gulou District.

Community 1 marked in orange was located in the southeast of Gulou District. This community was around Xinjiekou Huaqiao Road area, which is an important business district in Gulou District mentioned above and also an area with some strong strength stations. There were a few stations in this community, and the stations were sparsely distributed. There were no stations with weak strength, which indicated that Community 1 was an active one for the use of public bicycles.

Community 2 marked in red was located in the north of Gulou District. It contained the most stations, which were sparsely distributed. More than 90% of these stations had weaker strength than the average, which showed that Community 2 was mainly composed of stations with lower usage of public bicycles. No. 5 Ningxia Road Station, Tianfeigong Primary School Station, and other stations within the bottom ten stations in Table 3 belonged to this community.

Community 3 marked in green was located in the southwest of Gulou District. There were a few stations, and 70% of them had stronger strength than the average. This community contained many key stations, forming an area with high demand for public bicycles.

Community 4 marked in blue was located in the west of Gulou District. There were many stations and 65% of them had weaker strength than the average. The usage of public bicycles of Community 4 was only higher than that of Community 2.

Community 5 marked in purple was adjacent to Community 1, Community 3, and Community 4. It contained the fewest stations, which were densely distributed. Qingliangmen Suguo Supermarket Station, the station with maximum strength of the network, belonged to this community. Furthermore, Lixue Primary School Station, Huayang Jiayuan North Gate Station, and Jinxin Garden North Gate Station, which contributed the most to the strength of Qingliangmen Suguo Supermarket Station, also belonged to this community. Community 5 was an active one for the use of public bicycles.

Consistent with the analysis of Figure 5, the inactive Community 2 and Community 4 were in the north of Metro Line 4, while the active Community 1, Community 3, and Community 5 were in the south. The significant difference in the geographical distribution of communities confirmed that the stations with strong strength tended to cluster with stations with strong strength, and vice versa.

The PBN of Qixia District was divided into four communities (see Figure 8). Community 2 marked in orange had the most use of public bicycles, and Gate 1 of Maigaoqiao Subway Station belonged to this community. Community 4 marked in blue had the least use. Due to small population density, vast geographical area, and sparse stations, the usage of public bicycles was significantly lower than that of Gulou District. How to improve usage is an important issue for system operators.

**Figure 8.** The community distribution of the PBN of Qixia District.

#### **5. Conclusion**

Based on complex network theory and geographic visualization method, we constructed the regional PBNs using Gephi software and analyzed degree, strength, radiation distance, and community structure to understand the internal relationship of the PBSs, and we got the following conclusions:

Changes in the structure of PBNs over time will be studied in the future.

**Author Contributions:** Conceptualization, Y.Y.; Data curation, L.T.; Project administration, Y.Y.; Supervision, Y.Y.; Visualization, N.Z.; Writing – original draft, Y.Z.; Writing – review & editing, Y.Y., Z.L. and M.W.

**Funding:** The research is supported partially by the following: The National Natural Science Foundation of China (71690242, 71503132,<PHONE_NUMBER>0), the National Social Science Fund of China (No.18BTJ040), Qing Lan Project of Jiangsu Province, China (2017), Six talent peaks project in Jiangsu Province, China (JY-055), China Postdoctoral Science Foundation (2013M541697).

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).


**5. Conclusions**

The identification of β-tubulin bundles that surround the DNA nuclei in telophase suggests a mechanism of entrapment similar to a "hand-closure movement" that allows, along with the inter-MTOC spindle, the distribution of genetic material between the two newly formed nuclei.

The mitosis of *Entamoeba histolytica* trophozoites is a type of intranuclear pleuromitosis, closed or open? modified, since three spindles are formed: two radial and one inter MTOCs. In addition, these are found within the nucleus. It remains to be discovered if the spindle that apparently is outside the nucleus has a nuclear envelope or not.

**227**

**Author details**

Eduardo Gómez-Conde1

Luis David Gómez-Cortes4

Workers, Mexico City, Mexico

provided the original work is properly cited.

Autonomous University of Puebla, Mexico

of the National Polytechnic Institute, Mexico City, Mexico

Merciful Autonomous University of Puebla, Mexico

\*Address all correspondence to<EMAIL_ADDRESS>
\*, Miguel Ángel Vargas Mejía2

1 Laboratory of Research at Immunobiology, School of Medicine, Merciful

and Tayde Guerrero-González5

2 Molecular Biomedicine Department, Center for Research and Advanced Studies

3 Laboratory of Research at Experimental Immunology, School of Medicine,

5 Hospital "1ro of October", Institute of Security and Social Services for State

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

4 School of Biology, Merciful Autonomous University of Puebla, Mexico

, María Alicia Díaz y Orea3

,

*The Mitosis of* Entamoeba histolytica *Trophozoites DOI: http://dx.doi.org/10.5772/intechopen.88734*

*The Mitosis of* Entamoeba histolytica *Trophozoites DOI: http://dx.doi.org/10.5772/intechopen.88734*

*Parasitology and Microbiology Research*

KCL-hypotonization.

between the two newly formed nuclei.

**5. Conclusions**

envelope or not.

After karyokinesis, cytokinesis begins; the trophozoite with two nuclei begins to divide by narrowing the cytoplasm in its middle part [5]. This process is relatively slow and occurs gradually through stretching with intervals of rest. The cytoplasm of the middle part of the trophozoite thins until it forms a very thin filament which then breaks and results in two trophozoites of *Entamoeba histolytica* with a nucleus in each of them. It is still unknown whether cytoplasmic DNA [38] duplicates during mitosis of trophozoites or if it is only genetic material with other functions. The description and observations realized in the different phases of mitosis in *E. histolytica* trophozoites using the phase-contrast microscopy technique are consistent with those described by acridine orange vital staining and transmission electron microscopy [3–6]. Peripheral RNA chromatin and central DNA chromatin behaved in a similar manner to the acridine orange staining described [5]. The data described and observed with the anti-β-tubulin antibodies of *E. histolytica* regarding the radial microtubule bundles correlate with the observations described with transmission electron microscopy of nuclei in prophase and prometaphase [3, 4, 6]. However, there is a discrepancy about the number of spindles that are present and observed between the two nuclei in formation [2, 3, 6). The description of an inter-MTOC spindle independent of radial spindles was based on its observation with immunofluorescence (**Figure 8a**). An observation that brings forth new ways of studying the nuclear division in *E. histolytica* trophozoites is the presence of a green fluorescent internuclear cord obtained with the acridine orange staining and

The identification of β-tubulin bundles that surround the DNA nuclei in telophase suggests a mechanism of entrapment similar to a "hand-closure movement" that allows, along with the inter-MTOC spindle, the distribution of genetic material

The mitosis of *Entamoeba histolytica* trophozoites is a type of intranuclear pleuromitosis, closed or open? modified, since three spindles are formed: two radial and one inter MTOCs. In addition, these are found within the nucleus. It remains to be discovered if the spindle that apparently is outside the nucleus has a nuclear

**226**


*Review* **Experiences of Homeless Families in Parenthood: A Systematic Review and Synthesis of Qualitative Evidence**

**Filipa Maria Reinhardt Andrade 1,\* , Amélia Simões Figueiredo 2 , Manuel Luís Capelas 2 , Zaida Charepe 2 and Sérgio Deodato 2**

Received: 6 March 2020; Accepted: 7 April 2020; Published: 15 April 2020

**Abstract:** The objective of this systematic review was to identify the available qualitative data and to develop a framework to address the life experiences of homeless families in parenthood. The research was performed in the PubMed and CINAHL Complete databases, for works published in Portuguese, English, French and Spanish. Studies that included qualitative data, or both qualitative and quantitative data, were considered for this research. A total of 358 articles were obtained, of which 37 were assessed for eligibility, and 26 were rejected. In the end, 11 studies were selected. The Joanna Briggs Institute Critical Appraisal Checklist for Qualitative Research was used. These studies were conducted mostly in the United States, in temporary/transitional shelters for nuclear or single-parent families (led by women) in a homeless situation. In this context, the area which arose as the more relevant one was mental health, followed by the social studies. Two types of dimensions emerged from the results: mediating dimensions (which include the categories "Insecurity", "Lack of Privacy", "Isolation", "Stigma" and "Disempowerment") that are responsible for difficulties related to education, and behavioural changes in both the parents and the children; and supporting dimensions (which include the categories "Context as a Facilitator", "Relationship with Others" and "Parents' and children's Self") that lead to motivation, as well as the acquisition of strategies by the parents, to resolve parenting issues. This research helps expand nursing knowledge and presents a synthesis of the life experiences of homeless families in parenthood. Nursing can respond to the vulnerable population, due to its predominant role in promoting their health.

**Keywords:** family; homeless; nursing; parenting; parents; vulnerable population

### **1. Introduction**

Parenthood is considered "the recognition of a mother's/father's responsibilities, the assumption of behaviours that promote the children's growth and development, as well as the internalisation of expectations expressed by individuals, families, friends and society, regarding the parental role's appropriate or inappropriate behaviours"(own translation, from: Ordem dos Enfermeiros) [1] (p. 66). Parenthood is understood as a transition [2–4]. Life transitions correspond to periods of greater vulnerability and increased health risk, which is why they have been increasingly considered a central concept for nursing [2,5]. Nurses are aware of the needs and changes brought upon by transitions,

and they prepare the patient/family to better cope with such events, through learning and acquiring new skills [2].

The transition experience requires, as outcome indicators: the incorporation of new knowledge; the change of behaviours; the redefinition of the meanings associated with the occurred events; and, consequently, the redefinition of oneself within the social context [5]. Concerning possible constraints to the transition process, the author refers that, although community resources are able to create conditions which facilitate transition (family support, relevant information, referral, decision-making support), they may also create transition-inhibiting conditions (inappropriate counselling, insufficient information, etc.). The author points out that the society's development stage has a similar dual effect on transition—it may either facilitate the process, through the creation of laws and regulations, or inhibit it, through stigma, stereotypes, and marginalization [3].

In this regard, parenthood is considered to be an important, complex, challenging and highly responsible task for the human being, since it concerns the preparation of another human being for the challenges of development, namely physical, economical and psycho-social adversities [6]. While being an activity that usually involves the children, the parents and other family members in an interaction throughout life, it is not exclusive for these players and may involve other people, such as nurses, teachers, friends, partners, and even strangers [7]. In this sense, any person that participates in the care and development of a child is part of the parenthood process [8].  It is necessary to go through a complex, conscious—and sometimes unconscious—process of role appropriation. Although parenthood is a subjective concept, because it is influenced by cultural beliefs, the dimensions and structural tasks of the parent-child relationship tend to remain similar, thus allowing its assessment (i.e., the evaluation of parental skills and competences) and producing data adequate for research purposes [6]. In this sense, Cruz considers five assessable parental functions: (1) Satisfaction of the basic survival and health needs—Where he emphasizes that the inability to assume this function may be related to socio-economic constraints, natural disasters, drug addiction, or parents' disease; (2) Providing of an organized and predictable physical world for the child—Which includes safety-promoting routines (severely dysfunctional families reveal a great difficulty in performing this function); (3) Responding to the needs of cognitive understanding with respect to extra-family realities—Stresses the difficulty of families that are more isolated or less permeable in ensuring this function; (4) Satisfaction of the needs of affection, trust and safety—This function is associated with the construction of attachment, which has proved to be a fundamental predictor of personal adaptation throughout life; (5) Satisfaction of the child's social interaction needs—The family should perform this function because, as the original nucleus of the child's socialization, it influences the future integration of the child in broader social contexts [9].

Furthermore, Figueiredo uses the life cycle stages ("Family with young children", "Family with children at school", and "Family with adolescent children") to define several assessment categories with respect to the parental role's competence. The aforesaid categories differ in terms of knowledge dimension, as well as adhesion behaviour. This author relates the knowledge of the role with the available information and the ability to learn skills, in order to identify the need to acquire new knowledge conducive to behavioural changes. She also relates the adhesion behaviour dimension to those aspects which highlight the parents' actions that reflect the full incorporation of parenthood through the identity of the role. That incorporation is evidenced by trust and competence in the role's performance. The evaluative categories of knowledge and adhesion behaviour are related to: physical care (which includes nourishment, elimination, personal hygiene and physical exercise); leisure activities; health surveillance; safety and prevention of accidents; attachment; cognitive, psychosexual, emotional and social development; structuring rules; a positive interaction with the child; adaptation to school; and the parents' involvement in education [10].

When we observe the different conditions that should be involved in the parental process/activity, the complexity associated with the process of educating a child becomes evident. In this sense, family

plays a key role: it constitutes the most immediate space for the child's care, affections, dependence and socialization; it defines habits, health care routines, education, and the contexts to which the child is exposed (friends, school, neighbourhood, etc.); and it influences the present, the future and the development of the child. However, the family is not always able to provide a homogeneous environment and can have a negative impact on the child's well-being [11].

Within the family, there may be risk factors (internal or external), which represent a deficit in the children's development potential. On the other hand, the existence of protective factors (internal or external) that encourage the full development of the child can also occur. The internal protection factors relate to the quality of the interactions between family members. or to the involvement in stimulant activities. The external protective factors are associated with socioeconomic patterns, such as the family's structure, the parents' adequate working conditions, or the social support provided by public policies. As for external risk factors, they are related to demographic variables (e.g., having a single/adolescent mother, father's absence, separations and divorces) and to socioeconomic patterns (e.g., poverty, inequalities, mother's lack of education, violence, lack of social support, and restricted access to public policies regarding health and education). In contrast, the internal risk factors are associated with parental practices and parent-child interaction styles (e.g., abuse, neglect, negative communication, inconsistent discipline) [11]. In homeless families, many of those internal and external risk factors are simultaneously present, which accounts for their greater vulnerability [12]. From a nursing care perspective, vulnerability has always been considered a priority. As such, these families are a focus of interest for the nursing practice, often being the target of the aforementioned care [13].

A homeless person is an individual who, "regardless of his/her nationality, racial or ethnic origin, religion, age, sex, sexual orientation, socio-economic status, and physical and mental health status, is: homeless, living in a public space, in an emergency shelter, or in a precarious location; or homeless, living in a temporary accommodation destined for that purpose" (own translation, from: Ministério do Trabalho, Solidariedade e Segurança Social) [14] (p. 3925).

The reasons for the families' homelessness are different from those that lead to homelessness in adults. Most families are left homeless by: domestic violence [15–17]; repeated episodes of trauma and violence throughout life; child abuse; relationship breakups [15,16]; neighbourhood harassment; mental health problems involving parents and/or children [15,16,18]; special educational needs [15,16]; lack of family and social support networks; lack of access to statutory services [15–17,19]; social and emotional problems [17,20]; chronic instability; compromised health [19]; family head with a physical disability, with chronic health problems or with mental health problems [17]; poor financial situations and/or low income streams [21]; precarious housing situations; financial problems due to underemployment or unemployment; past mistakes (e.g., high school or college dropouts); and premature responsibilities, such as assuming a parental role at a young age [19]. The characteristics of these homeless families are heterogeneous. The most common are single-parent families led by (single) women [16,17,22]; with two children, generally under 11 years of age [16].

The lack of housing brings high social costs [23] and in families, has profound consequences, including the risk of health deterioration in family members [24,25]; the disruption of family dynamics, and the separation of parents and children [25]. Homeless families present multiple problems and needs that are interrelated (e.g., social, educational and health care) [15]. Homelessness is rarely an isolated event. Children from homeless families are prone to have a history of: low birth weight; anaemia; tooth decay; delayed immunizations; growth deficits; increased accident frequency, mainly injuries and burns [16]; developmental deficits; mental health problems [16,24,26,27]; behaviour disorders (e.g., sleep disorders, eating disorders, aggression and hyperactivity in young children); anxiety and post-traumatic stress [16]. A combination of multiple adverse childhood experiences may weaken their resilience [28] and they may become homeless as adults [28,29].

The protective factors for children belonging to homeless families include: school, due to its social stability, its routines and the parents' sense of achievement when they are capable of maintaining their child in the same school [16]; and the positive relationships between parents and children, which can

mitigate the negative effects of homelessness in childhood, by helping the children to better manage their emotions, by promoting self-regulation, by forming positive relationships and by improving the children's functioning [30].

Homeless families face unique conditions that can affect the health and well-being of both the parents and the children. They may also affect parental practices, a better understanding of the homeless parents' life experiences being necessary in order to increasingly meet the real needs of this population. The Canadian Homeless Press Observatory argues that the support given to families, through the strengthening of relationships, is essential to avoid situations of homeless youth [29].

The European Federation of National Organisations Working with the Homeless (*Fédération Européenned' Associations Nationales Travaillant avec les Sans-Abri*—FEANTSA) suggests future research, highlighting the importance of studies in the following areas: homeless families, in order to further unveil the existing challenges and the strategies to be implemented, concerning the relationship with these families; parenting, in order to identify the constraints and strategies that homeless women (and men) face in their parental roles, as well as in the construction of their parental identities [31].

A preliminary search in the PubMed and CINAHL databases revealed the inexistence of systematic reviews on this topic and that none is currently in progress. Hence the necessity of aggregating knowledge to better comprehend the parental experiences of homeless individuals, and to identify useful factors for the monitoring of these vulnerable families. This will contribute to the understanding of how professionals can support families in managing their situation.

It is important to highlight the importance of this work for the scientific area of nursing, since nurses are considered the health professionals closest to the population, playing a fundamental role in health promotion and disease prevention, especially among the vulnerable population, as is the case of homeless families. This work is part of the Special Issue of the International Journal of Environmental Research and Public Health, since it emphasizes the importance of nursing for society as promoters of the population's health.

In this sense, we decided to conduct this systematic review, in order to better recognize the main research lines that have been explored up to this date, and to respond to the challenge proposed by the FEANTSA. For that purpose, we employed a scientific methodology which follows the Joanna Briggs Institute (JBI) protocol for systematic reviews of qualitative evidence [32].

The objective of this systematic review was to identify available qualitative evidence and to develop a framework to address the life experiences of homeless families in parenthood. We intended to answer the following research question, formulated according to the PICo acronym, [32] (Population, phenomenon of Interest and Context): What are the parenthood (I) experiences of the homeless (C) family (P)?

### **2. Methods**

This systematic review adopts the method suggested by Moher, Liberati, Tetzlaff, Altman and the PRISMA group [33].

### *2.1. Inclusion Criteria*

*Population—*This review considered all the studies that focus on homeless families constituted by adult parents (over 18 years of age) and their children (under 18 years of age). The parents and/or family correspond to the individuals who are responsible for providing care to the child/adolescent [32]. The following types of family were included: nuclear family (a man and a woman, who may or may not be legally married, with one or more biological/adopted children); reconstructed family (a couple in which at least one of the elements had a previous marital relationship and has a child who resulted from that relationship); single-parent family (a single parent and one or more children, being identified the gender of the person who represents the parental figure); extended family (a nuclear family, plus other relatives, or people who share with them bonds other than kinship) [10].

*Phenomenon of interest*—This review considered all the studies that address the parenthood experiences of homeless families, with parenthood being based on the evaluative categories of the parental role proposed by Figueiredo [10], and also the five parental functions of Cruz [9].

*Context*—This review considered studies conducted with homeless families. To that end, we employed the definition of "Homeless" recommended by the ENIPSSA [14].

*Type of studies*—Primary studies, of mixed or qualitative nature, published in Portuguese, French, English and Spanish, without a previously defined time span.

### *2.2. Exclusion Criteria*

We excluded text (review) articles, opinion articles, letters to the editor, response letters, dissertations and reports, since priority was given to the numerous original research articles.

### *2.3. Search Strategy*

The research strategy that was used aimed to find published studies indexed in certain databases. It comprised three stages. The first stage included an initial search in the PubMed and CINAHL databases, to analyse the keywords; it also encompassed the analysis of the MeSH Health Sciences descriptors in the respective query platform, as well as in CINAHL. The MeSH terms were then used in the PubMed database, while the corresponding MeSH headings were used in the CINAHL database. After selecting the relevant Boolean operators, descriptors, and indexed terms used to describe them, a second search was conducted in all the included databases—PubMed and CINAHL Complete (through EBSCOhost). The keywords which were used corresponded to the ones defined according to the PICo acronym (**P**opulation, phenomenon of **I**nterest and **C**ontext). The research strategy was sensitive to the specific characteristics of each selected database (Table 1).

**Table 1.** Search strategy.

The searches were carried out between January 9th and January 30th, 2019. Duplicates were removed and, subsequently, two independent reviewers performed an analysis of the terms and descriptors found in the titles and abstracts of the articles. Studies that did not meet the inclusion criteria were excluded. Afterwards, the selected articles were read in full. Those that did not satisfy the inclusion criteria, or corresponded to the exclusion criteria, were eliminated. Finally, in a third stage, the selected articles' bibliographic references were analysed, in order to identify additional relevant studies. This review was not recorded in any systematic review database.

Before their integration in the final sample, all the selected articles were subjected to a methodological quality assessment.

### *2.4. Evaluation of the Methodological Quality*

The methodological quality evaluation was conducted by two independent reviewers, using the JBI Critical Appraisal Checklist for Qualitative Research [32]. Disagreements between the reviewers were resolved through debating. The evaluation's purpose was to analyse the strengths and weaknesses of each selected work. The reviewers critically appraised the articles, which were accepted for inclusion if there was congruence between the research methodology, the research's objectives, and the methods used for data collection, representation and analysis. *Int. J. Environ. Res. Public Health* **2020**, *17*, x FOR PEER REVIEW 6 of 15 *2.4. Evaluation of the Methodological Quality*  The methodological quality evaluation was conducted by two independent reviewers, using the

JBI Critical Appraisal Checklist for Qualitative Research [32]. Disagreements between the reviewers

weaknesses of each selected work. The reviewers critically appraised the articles, which were

Data was extracted from all the works included in the review, using the JBI-QARI standardized

objectives, scientific area, type of study (design and data collection method), population, context,

#### *2.5. Data Extraction* were resolved through debating. The evaluation's purpose was to analyse the strengths and

Data was extracted from all the works included in the review, using the JBI-QARI standardized data extraction tool [32]. The extracted data encompassed specific details about each research's objectives, scientific area, type of study (design and data collection method), population, context, phenomena of interest, and significant findings for our research question and objective. accepted for inclusion if there was congruence between the research methodology, the research's objectives, and the methods used for data collection, representation and analysis. *2.5. Data Extraction*

#### *2.6. Data Synthesis* data extraction tool [32]. The extracted data encompassed specific details about each research's

The qualitative research's results were grouped and categorized based on the similarity of meaning, with at least two findings per category, using the JBI-QARI tool [32]. The different categories were created through a process of consensus between the reviewers. Data was then aggregated and subjected to synthesis, resulting in a single comprehensive set of findings that can provide a basis for evidence-based practice. The findings were classified as "credible" or "unquestionable" (according to their credibility level), using the JBI-QARI tool. phenomena of interest, and significant findings for our research question and objective. *2.6. Data Synthesis*  The qualitative research's results were grouped and categorized based on the similarity of meaning, with at least two findings per category, using the JBI-QARI tool [32]. The different categories were created through a process of consensus between the reviewers. Data was then aggregated and subjected to synthesis, resulting in a single comprehensive set of findings that can

#### **3. Results** provide a basis for evidence-based practice. The findings were classified as "credible" or "unquestionable" (according to their credibility level), using the JBI-QARI tool.

We obtained a preliminary total of 358 articles through the database search. After duplicate removal, 349 works were subjected to relevance assessment based on their title and abstract. Of these, 248 were excluded after title evaluation and 64 were excluded after abstract evaluation, because they did not meet the established inclusion criteria. The remaining 37 studies were subjected to an eligibility assessment, and 26 were rejected, since they did not meet the inclusion criteria. Thus, a total of 11 articles were subjected to critical evaluation, with none being excluded. Figure 1 shows a PRISMA flowchart of the studies' identification and selection process for inclusion in the review. **3. Results** We obtained a preliminary total of 358 articles through the database search. After duplicate removal, 349 works were subjected to relevance assessment based on their title and abstract. Of these, 248 were excluded after title evaluation and 64 were excluded after abstract evaluation, because they did not meet the established inclusion criteria. The remaining 37 studies were subjected to an eligibility assessment, and 26 were rejected, since they did not meet the inclusion criteria. Thus, a total of 11 articles were subjected to critical evaluation, with none being excluded*.* Figure 1 shows a

PRISMA flowchart of the studies' identification and selection process for inclusion in the review.

**Figure 1.** PRISMA flowchart detailing the search's results and the studies' selection/inclusion process (based on the method suggested by Moher, Liberati, Tetzlaff, Altman and the PRISMA group) [33].

### *3.1. Methodological Quality*

All the 11 selected works were included in the analysis. These studies met the inclusion criteria and were considered methodologically rigorous, regarding the evaluation criteria. They offered useful descriptions of the daily life of homeless families. They also showed congruence between the research methodology, the research's objectives, the methods used for data collection, representation and analysis, and the methods employed to interpret the results. Most of the data represented the participants' opinions adequately. Despite the high quality of the selected articles, there was a lack of information in some of them. For instance, only 18% presented a statement contextualising the researchers' cultural and/or theoretical background. Furthermore, only 54.55% of the reported conclusions were derived from data interpretation. Prior to the critical evaluation, the reviewers decided that these shortcomings were not essential criteria that needed to be met for the article's inclusion. Table 2 presents the final assessment of the included works, specifying the research design's accuracy, as well as the quality of the resulting reports.

**Table 2.** Final evaluation of the included studies (according to the method used by Lockwood) [32].

N: No; NC: Not Conclusive; Y: Yes.

Q1. Is there congruence between the declared philosophical perspective and the research methodology? Q2. Is there consistency between the research methodology and the research's question(s)/objective(s)? Q3. Is there consistency between the research methodology and the data collection methods? Q4. Is there congruence between the research methodology and the data's representation and analysis? Q5. Is there congruence between the research methodology and the results' interpretation? Q6. Is there a statement that contextualises the researcher from a cultural or theoretical point of view? Q7. Are the researcher's influence in the research and the inverse phenomenon addressed? Q8. Are the participants and their opinions adequately represented? Q9. Is the research considered ethical, according to the current criteria, or, for recent studies, is there evidence of ethical approval by an appropriate committee? Q10. Do the conclusions drawn in the research report derive from the data's analysis/interpretation? Note: Q1, Q2, Q3, etc., refer to the questions included in the JBI Critical Appraisal Checklist for Qualitative Research [32].

Regarding the CONQual results, most of the selected studies obtained a moderate score [37–40,42], four reached a high score [15,25,34,36], one obtained a low score [35], and one achieved a very low score [41]. Despite their low classification, these last two articles were not eliminated, because their findings were unique and contributed to the knowledge of the phenomenon. Additional details can be seen in Tables S1 and S2, which are available in electronic format.

### *3.2. Results of the Extracted Data*

Concerning the research design, the studies are mostly qualitative in nature [15,25,34,35,38–40,42]. Only three works present a mixed nature, with qualitative and quantitative approaches [36,37,41]. Two of the articles are grounded in theory [38,39], while the remaining did not declare any specific methodology, merely stating that they used a qualitative approach. The methods applied in the 11 articles were diverse, namely: qualitative individual interviews, family interviews, focus groups with parents, participant observation, diaries and reflection activities.

The works are scattered over time (from 1997 to 2018). After the first article, which appears in 1997, there is a large gap, whilst the remaining articles were published between the time period 2003 to 2018. The first article that appears after this gap is the nursing study. They were mainly conducted in the United States, except for two studies that were performed in the United Kingdom [15,41] and one study that was carried out in Australia [40]. The context of the studies corresponded to temporary/transitional shelters for nuclear families [15,25,34,36,37,41] or single-parent families led by homeless women [35,38,42]. Only one study was conducted in multiple contexts (shelters, motels and transition houses) for homeless nuclear families [39]. Another research was carried out with single-parent families led by homeless men, who were recruited for the study by agencies that provide support to the homeless [40].

As for the number of families interviewed, the majority were single-parent families led by women, with a total of 506 families, and in two studies the number of interviews was not mentioned [35,38]. Next, the largest number of records were single-parent families led by men with a total of 51 interviews, 40 of whom were part of the same study [40]. Finally, there were 22 nuclear families (couple with children) in two of the studies [15,41], and five interviews that were represented by relatives in one of the studies [39].The most frequent research field was mental health [15,25,35–37,41], followed by social sciences [34,38,40], occupational therapy [42], education (in one of the psychology studies) [35], and nursing [39]. Further details about the included studies are presented in Table S3 that will be available in electronic form.

### *3.3. Synthesis of the Qualitative Research's Results*

Taking into account the objective of the study, which sought to develop a structure to address the experiences of homeless families in parenthood, we extracted a total of 74 results from the 11 studies. Those findings were combined to form 12 categories based on similarity of meaning. The categories were grouped into two dimensions: "Parenthood Mediating Dimensions" and "Parenthood Supporting Dimensions". As mediating dimensions, we considered situations of transition to a higher parenthood stage, where the transition's inhibiting factors are highlighted. As supporting dimensions, we considered situations which reveal the transition process, emphasising the facilitating resources for that transition. The mediating dimensions include the categories "1—Insecurity", "2—Lack of Privacy", "3—Isolation", "4—Stigma", and "5—Disempowerment", which support the categories "6—Education Difficulties", "7—Changes in Parents' Behaviour", and "8—Changes in Children's Behaviour". On the other hand, the supporting dimensions include the categories "9—Context as a Facilitator", "10—Relationship with Others", and "11—Parents' and Children's Self", which lead to the additional category "12—Parenting Motivation and Strategies" that addresses parenting issues.

Next, we will present the synthesis of our findings, in the form of a narrative text, followed by an overview of the obtained results associated with the aforesaid findings and the established categories.

### *3.4. Synthesis of the Findings*

### 3.4.1. Parenthood Mediating Dimensions

This synthesis derives from 53 findings and the following eight categories: "Insecurity", "Lack of Privacy", "Isolation", "Stigma", "Disempowerment", "Education Difficulties", "Changes in Parents' Behaviour", and "Changes in Children's Behaviour".

The mediating dimension of the "Insecurity" category is sustained by the following findings: lack of security; lack of hygiene; racism; intimidation; attacks from shelter residents; and negative influences from others. In the "Lack of Privacy" category, it is supported by: space limitations; restrictive environment; and the need for privacy to play. In the "Isolation" category, it is sustained by: shelters located far from family, school and city centre; separation from friends and family; distancing from children; and the existence of loneliness feelings. In the "Stigma" category, it is supported by: feelings of stigmatization, humiliation, disrespect, and judgment. The "Disempowerment" category is divided into 3 subcategories: "Routine Change", sustained by the changes in the shelter's routines, the difficulty in maintaining routines, and the involvement of other adults; "**Rule Enforcement**", supported by shelter rules not consistent with previous parenthood options, as well as by the imposition of external rules; and "Parents' Needs", sustained by the need for practical, material and financial help, employment, education, transport, housing assistance, mental health promotion, pregnancy support, and time for oneself and one's children, as well as by the inability to play the role of provider and guide. The "Changes in Children's Behaviour" category includes: mental health problems; disobedience; mood swings; disrespect for authority; aggression; feelings of anguish, boredom and confusion; eating disorders; development regressions; concerns; and hiding the reality of living in shelters. The "Changes in Parents' Behaviour" category encompasses the lack of availability and conditions to meet the child's needs, as well as the dependence on the shelter's resources. Finally, the "Education Difficulties" category includes: difficulty in establishing discipline; the need for help when dealing with school; difficulty in integrating the school's community; difficulty in identifying school absenteeism as a problem; inability to help the child with school tasks, to maintain the child in a single school system throughout the year, and to identify academic problems; abdication of the responsibilities concerning school; absence of regular school attendance; and education barriers related to communication.

### 3.4.2. Parenthood Supporting Dimensions

This synthesis derived from 21 findings and 4 categories: "Context as a Facilitator", "Relationship with Others", "Parents' and Children's Self", and "Parenting Motivation and Strategies". It demonstrates that the homeless situation experienced in temporary/transitional shelters seems to enhance parenthood issues in some families, since they lead to motivation and acquisition of strategies by the parents, in order to deal with those issues. Some parents perceive this "Context as a Facilitator", because: it gives them access to services and resources; it is a safe place; it strengthens family practices and cohesion; and it is a stabilising experience that highlights the parental role. Additionally, they consider that it promotes the "Relationship with Others", defending that: it is a social opportunity; it provides a sense of community and of collective parenting; it provides supportive relationships, positive encounters with community service providers, and social support from family and friends. In addition, it seems to encourage the "Children's Self", since a young person demonstrated having resilience and perseverance, despite being homeless. It also seems to promote the "Parents' Self", since they reveal: the ability to help their children to deal with emotions; the ability to identify academic problems; optimism; hope for the future; perseverance; self-efficacy; resilience; resistance; the ability to set goals; and that they can do without help. Despite the homelessness situation, in some families parenthood seems to be enhanced, and it is even verified that the children function as a source of "Motivation", leading parents to seek improvement regarding their life situation and employment status, as well as to seek help to promote their mental health and maintain their morale. Parenthood also appears to feed the desire to move forward, in order to provide a better life for the respective children. Furthermore, to cope with the various challenges, the parents seek "Strategies", such as: reading; writing a diary; keeping focus; attending church; and talking to the respective support team, friends and family.

Figure 2 shows the relationship between the categories and the synthesised findings, to illustrate the general synthesis process.

#### *Int. J. Environ. Res. Public Health* **2020**, *17*, 2712

*Int. J. Environ. Res. Public Health* **2020**, *17*, x FOR PEER REVIEW 10 of 15

**Figure 2.** Overview of the synthesised findings. **Figure 2.** Overview of the synthesised findings.

#### **4. Discussion 4. Discussion**

This systematic review sought to gather the best available evidence on the parenthood experiences of homeless families. As stated previously, the aggregation of 11 qualitative research articles resulted in the finding of two types of parenthood dimensions. On the one hand, we found "Parenthood Mediating Dimensions" (corresponding to transitional states), which include: "Insecurity", "Lack of Privacy", "Isolation", "Stigma", and "Disempowerment" (the latter pertaining to routine changes, rule enforcement and the multiple needs of the parents). On the other hand, we found "Parenthood Supporting Dimensions", which encompass: "Context as a Facilitator" (of access to services and resources, by acting as a stabilising experience for the family, and by highlighting the parental role), "Relationship with Others", and finally the "Parents' and Children's Self". In their turn, these categories led to relevant findings. The "Parenthood Mediating Dimensions" sustain changes in the parents' and children's behaviour, but, above all, they are associated with difficulties in education. Conversely, the "Parenthood Supporting Dimensions" lead to motivation and to the This systematic review sought to gather the best available evidence on the parenthood experiences of homeless families. As stated previously, the aggregation of 11 qualitative research articles resulted in the finding of two types of parenthood dimensions. On the one hand, we found "Parenthood Mediating Dimensions" (corresponding to transitional states), which include: "Insecurity", "Lack of Privacy", "Isolation", "Stigma", and "Disempowerment" (the latter pertaining to routine changes, rule enforcement and the multiple needs of the parents). On the other hand, we found "Parenthood Supporting Dimensions", which encompass: "Context as a Facilitator" (of access to services and resources, by acting as a stabilising experience for the family, and by highlighting the parental role), "Relationship with Others", and finally the "Parents' and Children's Self". In their turn, these categories led to relevant findings. The "Parenthood Mediating Dimensions" sustain changes in the parents' and children's behaviour, but, above all, they are associated with difficulties in education. Conversely, the "Parenthood Supporting Dimensions" lead to motivation and to the acquisition of strategies by the parents, with respect to parenting issues.

acquisition of strategies by the parents, with respect to parenting issues. We found that some of the considered dimensions fit into the concept of parenthood recommended by the International Council of Nurses [1], as well as into the one suggested by Figueiredo [10]. Nevertheless, most of the dimensions corresponded to experiences, or feelings, reported by the parents. Some reflected difficulties in exercising the parental role, while others revealed protective factors related to the homelessness situation. This was one of the limitations we encountered in this study. In the "Parenthood Supporting Dimensions", the transition process is revealed through: the need of establishing relationships with others, as sources of support and information; the interaction with others; and the use of resources and coping strategies, to deal with We found that some of the considered dimensions fit into the concept of parenthood recommended by the International Council of Nurses [1], as well as into the one suggested by Figueiredo [10]. Nevertheless, most of the dimensions corresponded to experiences, or feelings, reported by the parents. Some reflected difficulties in exercising the parental role, while others revealed protective factors related to the homelessness situation. This was one of the limitations we encountered in this study. In the "Parenthood Supporting Dimensions", the transition process is revealed through: the need of establishing relationships with others, as sources of support and information; the interaction with others; and the use of resources and coping strategies, to deal with the situation. This is in line with the findings presented by Meleis [3].

the situation. This is in line with the findings presented by Meleis [3]. We encountered another limitation in this study, related to the context of the included works (all were conducted in temporary or transitional shelters). The research should be extended to other contexts of homelessness, such as: the street/public spaces, precarious locations, pensions, and rooms paid for by the social services. We encountered another limitation in this study, related to the context of the included works (all were conducted in temporary or transitional shelters). The research should be extended to other contexts of homelessness, such as: the street/public spaces, precarious locations, pensions, and rooms paid for by the social services.

We also found that the families identified in the study fit the characteristics of the different types of homeless families, such as single-parent families led by (single) women [16,17]. Additionally, we We also found that the families identified in the study fit the characteristics of the different types of homeless families, such as single-parent families led by (single) women [16,17]. Additionally, we identified multiple problems and needs in the studied families, which is in accordance with the results obtained by Anderson et al. [15], as well as multiple risk/protection factors (both internal and external), in line with the findings of Macana and Comim [11].

Regarding the limitations of this review, we stress that only articles published in English, Portuguese, French and Spanish were included, and there might have been relevant findings in works published in other languages. Another limitation relates to the use of a small number of databases, since its extension would have led to a broader research, and to the possibility of including other significant contributions. Another possible limitation concerns the priority given to the search for articles, thus excluding other kinds of text, such as opinion documents, dissertations and reports. Since the literature available for inclusion was limited to published original research articles, there is always the risk that relevant studies may not have been identified.

Despite the effort to find all relevant articles, some significant research works may have been overlooked. There is the possibility that both reviewers may have neglected important studies, during the screening process of the 358 articles initially obtained. On the other hand, the bibliographic search allowed the identification of articles produced in various professional fields, such as psychiatry, psychology, social sciences, occupational therapy, and nursing. This provided a broader picture of the homeless parents' experiences.

Some of the obtained articles corresponded to secondary findings related to the parenthood experiences of homeless families, being thus included in the review. For instance, the purpose of one of the selected articles was to identify the parents' and the employees' perceptions, regarding their experience with the family support team, and also to recognise ways of improving this service in the future [15]. Although the focus was on the experience with the family support team, some of this study's findings were considered relevant to the objective of the present systematic review, being, therefore, included in it. This would not have been possible using a more restrictive bibliographic search strategy.

When we critically evaluated the 11 included articles, they revealed a variety of strengths and limitations. All works showed coherence between the research methodology and the research's question(s)/objective(s), the data collection methods and the results' interpretation. Nonetheless, two of the studies did not present congruence between the stated philosophical perspective and the research methodology [35,39], and there were two articles that did not present congruence between the research methodology and the data's representation and analysis [35,41].

The absence of an appropriate statement enhanced the complexity of evaluating the congruence between the philosophical perspective and the research methodology. Additionally, the inexistence of congruence, regarding the data's presentation and analysis, increased the difficulty of the data's evaluation. Although the reviewers did not consider these phenomena a reason for exclusion, the congruence between the philosophical perspective and the research methodology, as well as between the research methodology and the data's representation and analysis, would have been preferable, to strengthen the studies' credibility.

Data were collected through participant observation, individual interviews, written diaries, reflection activities, and group interviews/focus groups. The fathers' perspectives were under-represented, because most of the interviewees belonged to single-parent families led by women, thus highlighting the perspective of homeless mothers. However, in one of the studies, it was possible to analyse exclusively the male perspective, since it encompassed single-parent families led by men [40]. This unequal representation might be considered a limitation, because homeless fathers may have different experiences from homeless mothers. Even so, it may provide a realistic picture of homeless families.

Most of the studies were conducted in the United States, except for two which were carried out in the United Kingdom [15,41], and one that was performed in Australia [39]. This geographical distribution can result in limitations related to cultural differences, concerning the way homeless parenthood is viewed. It is important to note that these results can also refer to refugee families, which are becoming more important today. Such divergences may be relevant, since they can have implications for the practice in various settings and cultures. Nonetheless, we consider the studies' heterogeneity a strength, because it represents the complexity and diversity of the parenthood experiences in homelessness situations.

### **5. Conclusions**

This review's findings contributed to the scientific knowledge about the complexities of homeless families/fathers/mothers and the challenges faced by them. Homeless parents living in temporary or transitional shelters are confronted with the intricacy of parental experiences influenced by insecurity, lack of privacy, isolation, stigma and disempowerment. On the other hand, to some families, the homelessness experience lived in temporary or transitional shelters seems to enhance parenthood, since they regard that context as a facilitator of the parental role, which promotes family cohesion, the relationships within the family and with others, as well as the parents' and the children's self. During the complicated journey of homeless parenthood, the parents use coping strategies and see their children as a great source of motivation, where they find strength to fight against the multiple difficulties they experience.

This review adds scientific knowledge on the experiences of homeless families, by revealing several parenthood mediating and parenthood supporting dimensions. However, the specific knowledge about parental experiences is still limited. The concept of homeless parenthood is scarcely researched; there exists a need for further studies in other homeless contexts, and in the field of Nursing, in order to adapt nursing responses to those families. While conducting this review, we found a reduced number of articles about the studied topic, which justifies the presented need and encourages additional research in the area of homeless parenthood. We stress the need for further research on paediatric nursing care, in the above-mentioned area. Regarding our methodological approach, we conclude that it was appropriate, since it allowed answering the research question.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/1660-4601/17/8/2712/s1, Table S1. Final evaluation of the included studies (according to the method used by Lockwood), Table S2 Summary of the conclusions reached through the CONQual tool (adapted from the one proposed in the Joanna Briggs Institute's Methodological Manual), Table S3. Characterization of the included studies.

**Author Contributions:** Conceptualization, F.M.R.A. and A.S.F.; methodology, F.M.R.A., A.S.F., M.L.C. and Z.C.; software, F.M.R.A., A.S.F. and M.L.C.; validation, F.M.R.A., A.S.F.; formal analysis, F.M.R.A., A.S.F.; investigation, F.M.R.A., A.S.F., M.L.C., Z.C. and S.D.; resources F.M.R.A., A.S.F., M.L.C., Z.C. and S.D.; data curation, F.M.R.A., A.S.F., M.L.C. and Z.C.; writing—original draft preparation, F.M.R.A. and A.S.F.; writing—review and editing, F.M.R.A. and A.S.F.; visualization, F.M.R.A., A.S.F., M.L.C., Z.C. and S.D.; supervision, F.M.R.A., A.S.F., M.L.C., Z.C. and S.D.; project administration, F.M.R.A. and A.S.F.; funding acquisition, S.D. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by Universidade Católica Portuguesa—Centre for Interdisciplinary Research in Health (CIIS).

**Conflicts of Interest:** The authors declare the absence of any conflicts of interest.

### **References**

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

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Biochemical Toxicology - Heavy Metals and Nanomaterials

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