Discussion
cardiometabolic
RECRUITMENT
This paper reports on costs, feasibility and results of used recruitment strategies, baseline characteristics of the study sample, potential sociodemographic differences in successful recruitment strategies and feasibility of cardiometabolic measurements at home. The results indicate that letters/flyers sent to home addresses and distributed in the supermarkets recruited most participants. Supermarket flyers were the cheapest and least time-invasive of all paid recruitment strategies. The social media campaign was the most expensive, and mailings of recruitment letters and in-store-recruitment were the most time-invasive and therefore costly in terms of recruited staff hours. Flyers in the supermarket and media news articles seemed to recruit relatively more females and word-of-mouth seemed to recruit relatively more males. At-home measurement of cardiometabolic markers was feasible, as they were successfully completed by most participants. Older participants had more often a failed first attempt of blood measurement, whilst younger participants were more often non-completers of the blood measurements.The success of mailing letters and flyers to home addresses and the distribution of flyers in the supermarket is likely due to their wide reach and the fact that these strategies were used early in the recruitment process. The fact that our social media campaign, which was used later, appeared very costly in terms of recruitment yield is in contrast to what other studies showed. In studies where social media were used as the primary recruitment method, it appeared (cost)-effective (e.g. ~6–14 Euros per included participant [The included study sample was comparable with the general Dutch population in terms of educational attainment, but females were overrepresented and participants scored relatively high on the DHD15-index. Overrepresentation of females in epidemiological studies is a well-known phenomenon [Our results suggested that passive recruitment strategies yielded more females whilst active strategies more males, which is also seen in other studies [The COVID-19 pandemic had a considerable impact on recruitment and data collection procedures. At-home measurement of cardiometabolic makers and self-installation of the coaching app may have been challenging for some participants, since participants were required to understand and be able to follow instructions from a written manual or video. Participants only received support from research staff when actively asking for it, which requires a certain level of self-efficacy. This may have led to some selection bias, resulting in a study sample consisting of participants with relatively high levels of self-efficacy. The at-home measurements may have introduced self-assessment bias and reduced measurement reliability for waist circumference measurement. Previous research has shown that especially those with lower educational attainment had relatively more often an overestimation of their waist circumference measurement, as well as younger versus older participants [We recruited participants in socially disadvantaged neighbourhoods via various passive and active recruitment approaches with the aim to recruit a relative high proportion of those with a lower and medium educational attainment [