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.