EPIC is among the largest cohort studies, with approximately 475,000 study participants, on the etiological influence of diet and chronic diseases. During a 4-year recruitment period, two German EPIC centers, located in Heidelberg and Potsdam, aimed to recruit a total of 60,000 study participants from the local populations. The recruitment process was based on addresses from general population registries and started 4-5 weeks in advance with an initial invitation by mail to the basic examination for this study. Subjects not responding within 2 weeks were reminded. In Potsdam, this was done by mail and telephone, and in Heidelberg by telephone. During the recruitment phase, from 1994 to 1998, 53,162 subjects in total were examined for the cohort studies in Heidelberg (n = 25,546) and Potsdam (n = 27,616). The participation rate, compared to the invited number of subjects, was 22.7% in Potsdam and 38.3% in Heidelberg, with a considerable variation by municipality and gender. A comparison with data from the National Health Survey 1991/1992 revealed that the cohort populations were of higher socio-economic status and were healthier than the source population. We concluded that the selective participation would help to ensure high maintenance of the cohort during active follow-up. Selective participation does not harm etiological conclusions because disease associations are derived internally as relative risk. The relative risk estimates can be used to calculate population-attributable risk and preventable proportion, based on exposure prevalence derived by surveys and other studies.
Copyright 1999 S. Karger AG, Basel