Mental disorders, attrition at follow‐up, and questionnaire non‐completion in epidemiologic research. Illustrations from the CoLaus|PsyCoLaus study

OBJECTIVE: This study aimed to investigate the associations between mental disorders recorded at baseline and participation in the subsequent follow‐up interview (vs. attrition) or baseline questionnaire completion (vs. non‐response) within the psychiatric arm of a population‐based study. METHODS: Participants of a physical health survey were initially invited to also participate in a semi‐structured interview covering mental disorders and were reassessed approximately 5.5 years later. They were also asked to complete self‐rating questionnaires at baseline. Associations between the presence of lifetime mental disorders assessed at baseline and attrition at follow‐up as well as non‐completion of self‐rating questionnaires at baseline were established. RESULTS: After controlling for sociodemographic variables, a significant negative association was found between anxiety disorders at baseline and attrition at follow‐up (Adjusted odds ratio (AOR) = 0.84; 95% confidence interval (CI) = 0.71–1.00) and a positive association between major depressive disorders (MDD) and non‐response to the self‐rating questionnaires at baseline (AOR = 1.24; 95% CI = 1.05–1.45). CONCLUSIONS: The associations of anxiety disorders during lifetime with a higher participation rate in interviews at follow‐up and of MDD during lifetime with the non‐completion of self‐rating questionnaires are potential sources of bias and should be taken into account in future longitudinal research.