Healthy worker effect: The occurrence whereby employed individuals tend to have lower mortality rates than those who are unemployed. The effect, which can pose the serious problem in the interpretation of industrial cohort studies, has two major components:

* selection at the recruitment to exclude the chronically sick resulting in low standardized mortality rates among the recent recruits to an industry,

* a secondary selection procedure by which workers who become un?t during employment tend to leave, again leading to the lower standardized mortality ratios among long- serving employees.