[The general population as a reference group. A discussion of the concept of the healthy worker effect]

In cohort studies concerning occupational diseases the general population is a commonly used reference entity in countries with national cancer registries or census bureaus. However, former and present employees regularly experience lower disease incidence than the general population, even in occupations with exposures known to cause adverse health outcomes. This phenomenon is often referred to as the "healthy worker effect". The concept is discussed in the present paper.