THE EVOLVING CONCEPT OF THE HEALTHY WORKER SURVIVOR EFFECT

The ''healthy worker survivor effect'' describes a continuing selectio n process such that those who remain employed tend to be healthier tha n those who leave employment. In an analysis of exposure response patt erns in an occupational study, the healthy worker survivor effect gene rally attenuates an adverse effect of exposure. In practical terms, su ch attenuation will be more problematic when evaluating subtle rather than strong associations. The use of an internal referent does not gua rantee elimination of this effect, since by definition, it manifests w ithin an occupational cohort. Although documented over 100 years ago, there is little consensus regarding the most appropriate method to con trol for: the healthy worker survivor effect. Four methods have been P roposed for its control: (1) restriction of the cohort to survivors of a fixed number Of years of follow-up, (2) lagging the exposure to exc lude recent exposure incurred by those who remained on the job, (3) ad justing for employment status as as a confounder, and (4) treating the healthy worker survivor effect simultaneously as an intermediate and confounding variable by means of the G-null test or its extension, G-e stimation analysis, using structurally nested failure time models. Thi s paper reviews the concept of the healthy worker survivor effect and the four methods to control for it.