Analysis of excess lung cancer risk in short-term employees.

An excess of lung cancer found in a cohort of 741 New York State tremolitic talc workers observed from 1947 through 1978 has been shown paradoxically to be concentrated in short-term workers. Review of past work histories suggests that the excess of lung cancer in these short-term workers may be accounted for by prior exposures rather than by exposures at the employment under investigation. This finding has significant implications in view of the developing practice of including short-term workers in occupational cohort studies in contrast to the more traditional practice of excluding short-term workers. The traditional practice was based on the assumption that the inclusion of short-term workers with little exposure, and thus little risk, might dilute an otherwise apparent association between mortality and exposure. This study suggests that in certain instances the inclusion of short-term workers may magnify rather than dilute the estimation of risk, reflecting the presence of confounding variables.