ABSTRACT
Background: The Genetic Links to Anxiety and Depression (GLAD) Study is a large cohort of individuals with lifetime anxiety and/or depression, designed to facilitate re-contact of participants for mental health research. At the start of the pandemic, participants from three cohorts, including the GLAD Study, were invited to join the COVID-19 Psychiatry and Neurological Genetics (COPING) study to monitor mental and neurological health. However, previous research suggests that participation in longitudinal studies follows a systematic, rather than random, process, which can ultimately bias results. Therefore, this study assessed participation biases following the re-contact of GLAD Study participants. Methods: In April 2020, all current GLAD Study participants (N = 36,770) were invited to the COPING study. Using logistic regression, we investigated whether sociodemographic, mental, and physical health characteristics were associated with participation in the COPING baseline survey. Subsequently, we used a zero-inflated negative binomial regression examined whether these factors were related to participation in the COPING follow-up surveys. Results: For aim one, older age, female gender identity, non-binary or prefer to self-define gender identity, having one or more physical health disorders, and providing a saliva kit for the GLAD Study were associated with an increased odds of completing the COPING baseline survey. In contrast, lower educational attainment, Asian or Asian British ethnic identity, Black or Black British ethnic identity, higher alcohol consumption at the GLAD sign-up survey and current or ex-smoking were associated with a reduced odds. For aim 2, older age, female gender, and saliva kit provision were associated with greater COPING follow-up survey completion. On the other hand, lower educational attainment, ex-smoking, higher alcohol consumption at the GLAD Study sign-up, and self-reported attention deficit hyperactivity disorder had negative relationships. Conclusions: Participation biases surrounding sociodemographic and physical health characteristics were particularly evident when re-contacting the GLAD Study volunteers. Future researchers re-contacting participants from existing cohorts/BioResources should be mindful of participation bias and how it may affect results obtained from analyses.