Strengths and limitations
Applying a mixed-method study design resulted in several advantages. While the quantitative analyses provided a general view of experiences and opinions, the qualitative analyses helped to understand the underlying reasons and conditions. The different data sources supported the multiplicity of perspectives so that the isPO OGs and the patients and professionals service providers articulated their views and experiences. Furthermore, a multi-contextual understanding was gained, as all isPO care networks were considered, and their similarities and differences were elaborated. The ability to synthesise these results helped draw useful recommendations for actions.The individual methods and data sources, respectively, contain strengths and limitations. Although the isPO care data contain representative data on the entire isPO care trajectory, they can also be afflicted with documentation gaps and errors. Moreover, the isPO OGs are obliged to conduct their assessment directly after the consultation, whereas the patients do so four months after enrolment in isPO. However, the data linkage with the patient survey data provided relevant information on the topics of satisfaction with the isPO OG consultation and social support. In addition, the quantitative patient data helped gain an overview of all patients, as they were not interviewed in focus groups, unlike the isPO OGs and professional service providers, and not all the patients interviewed had utilised an isPO OG consultation. The number of isPO OGs surveyed by questionnaire was very small in absolute terms. Hence, no parametric statistical evaluations were possible, but isPO was implemented in only four care networks during the project phase so that the population of isPO OGs is statistically small. No quantitative data on the isPO OG service was available for the professional service providers. Therefore, the qualitative data was a necessary complement to capture comprehensive insights from all perspectives. The qualitative data helped classify and explain the quantitative results. For example, the different utilisation rates in the care networks could be explained by the fact that, according to the qualitative investigations, there were different resources and attitudes on the part of the professional service providers, which in turn influenced the patient information on the isPO OG service and, thus, the utilisation decision of the patients.The isPO programme was implemented in only four care networks with a limited number of service providers. This resulted in partly the same participants within the interviews and focus groups. However, they took part in qualitative data collections at different time points so changes between the different implementation phases could be reflected.The mixed-methods design allowed for comprehensive evaluation (Borglin In addition, within the project duration of four years, isPO was not only developed but also implemented and optimised. This means that the isPO OG service only reached a high degree of maturity at the end of the project. Thus, short-term health effects could be observed, but not medium- and long-term ones. Moreover, depending on the assigned care level, patients took up further interventions in isPO, so it is very difficult to differentiate the effects of the individual interventions and, thus, also that of the isPO OG service after completion of the 12-month care. Therefore, qualitative data were also used to supplement the initial health effects key figures. For future projects on complex interventions, we recommend a two-step approach. First, a project should be carried out that includes implementation and formative evaluation. After reaching high maturity, the summative evaluation should take place as a separate project. For this, appropriate funding programmes are necessary that enable such an approach.