Strategies to enhance follow-up response in a cohort study with Berliners of Turkish descent

Abstract

Abstract Background Follow-up participation and retention are essential in long-term cohort studies. Loss to follow up may reduce the power of statistical analyses and external validity. The aim of this analysis was to evaluate the response after different contact methods in a cohort study with Berliners of Turkish descent and to compare characteristics of participants with those of non-participants. Methods In 2012-2013, Berliners with a Turkish migration background were recruited for this cohort study that initially aimed to examine recruitment strategies. The participants were contacted again 5 years later via postal mail and were asked to complete a questionnaire on the onset of new diseases and health care utilization. Written reminders, phone calls, and home visits were used to increase the response. Study documents were available in German and Turkish language. In descriptive analyses, we examined the response rate in relation to the recruitment approach. A regression analysis was conducted to investigate associations between individual, socioeconomic, and medical factors and the response. Results Out of 560 contacted persons, the neutral non-response (unknown address or death) was 13.6%. Of the remaining 484, 234 persons participated in the follow-up (women: 63.1%, mean age±SD: 49.8±12.6 years). The response was 16.1% after the first invitation letter, 24.2% after phone calls, 33.3% and 42.1% with a first and a second reminder letter, respectively, and 48.3% after home visits. The participants had more often German citizenship and a higher net income at baseline than non-participants. Migration generation, age, sex, education, and chronic diseases were not associated with participation (preliminary results). Conclusions In our participants with a migration background, every additional contact effort including home visits further increased cohort retention. Investing in comprehensive retention efforts may lead to studies that are more valid to examine the health of migrants. Key messages Investing in different contact efforts including reminder letters and home visits can improve follow-up response in longitudinal studies. Retention strategies should be used in longitudinal studies to increase statistical power and external validity.