Healthy worker effect in the total Finnish population.

The selection due to the "healthy worker effect" was estimated from a random sample of the total Finnish population. The sample of 20 000 people was followed for changes in occupations from 1960 to 1970 and for deaths in 1971-5. Those entering the active work force had a standard mortality ratio of 70, indicating a healthy population selection effect. Those staying in the same occupational category from 1960 to 1970 had a 20% lower mortality than those who did not. This survivor population effect was due to changes to another occupational group and to early retirement. These factors had an inverse effect on the survival history of an occupational group.