NON-PARTICIPATION IN THE SECOND WAVE OF THE PART STUDY ON MENTAL DISORDER AND ITS EFFECTS ON RISK ESTIMATES

Background: In epidemiological studies, analyses are needed to investigate the consequences of non-response. Aims: To analyse the consequences of attrition in the second wave of the population-based PART study, which was performed three years after the first wave. Methods: Potential determinants for non-participation obtained from population registers and the first wave were analyzed. The relationships between potential determinants and reduced well-being or depressive mood in the first wave questionnaire were investigated separately for participants and non-participants in the second wave. Samples of respondents to the second wave questionnaire with reduced or not reduced well-being were summoned for interview regarding determinants of distress and disorder. The occurrence of potential determinants was compared between participants and non-participants in both groups Results: Low income, low education, non-Nordic origin, not being married and previous psychiatric diagnosis were associated with lower participation rates. These variables were similarly related to depressive mood and low psychological well-being in the first wave among participants and non-participants in the second wave. Potential determinants were not or only weakly related to participation in the interview groups. Conclusion: Although the true prevalence of distress and disorder is underestimated, the true associations between potential determinants and the outcomes seem reasonably well reproduced.