The Zurich Study:: participation patterns and Symptom Checklist 90-R scores in six interviews, 1979-99

Objective: The Zurich study is a longitudinal study in psychiatric epidemiology that started in the late 1970s. The sixth interview in 1999 provides the basis to investigate and update the participation and drop-out patterns of the Zurich subjects. Method: Aside from descriptive analyses, particular attention was paid to the Symptom Checklist 90-R (SCL-90-R), used initially to stratify the Zurich sample. Results: The initial proportions of high-scorers vs. low-scorers (two-thirds vs. one-third) have not changed significantly in the 367 subjects who participated in the 1999 interview. More detailed analyses indicate a selective and changing dependence of participation/drop-out on health status as measured by the SCL-90R. In recent interviews drop-out has become more likely in subjects with extremely high SCL scores and in subjects with low SCL scores. Conclusion: Drop-out in the Zurich Study is associated with extreme SCL scores.