Original article

Scand J Work Environ Health 1982;8 suppl 1:30-33    pdf

Restricted cohort study designs.

by Oakes D, McDonald JC

Practical constraints may limit both cohort selection and the degree of follow-up in longitudinal studies of occupational mortality. For example, it may be possible to study only those men employed on a certain date or to trace (through pension fund records) only men employed at or close to normal retirement age or to follow men only for a very limited period after they have left employment. In an examination of the effects of such restrictions, advantage was taken of the availability of detailed work histories and the full follow-up of a large birth cohort of chrysotile asbestos workers. Age-matched case-referent analyses were performed under each type of restriction. All three analyses revealed the clear exposure-response relationship between cumulative dust exposure and lung cancer that was found in the full analysis. Most other findings were also not inconsistent with the earlier results. Such restricted cohort studies, with case-referent approaches to analysis can be justified in logic. The findings provide some empirical support for these methodological variants and suggest that they may be useful when complete follow-up of an entire birth cohort is not feasible.