Negative health selection into physically light occupations.

Health selection, which transfers workers with health problems from physically heavy to physically light occupations, may be a factor contributing to excessive morbidity in the latter group. The aim of this study was to investigate whether workers who had stopped doing heavy work and moved to occupations with low physical demand are generally more ill than workers who had always done light work. The study population comprised 5436 men and 5486 women aged 25 to 74 years, who were interviewed within the scope of the Statistics Sweden Survey of Living Conditions in the years 1977 and 1979-81. For all respondents detailed recording of the occupational histories was completed. For all the diseases and functional disorders studied an increase in risk could be seen for movers. Moreover, movers who had left their heavy work most recently had the greatest risks. This association was most apparent when studying musculoskeletal disorders and impaired working capacity for men and diseases of the circulatory organs and impaired hearing for women. The findings indicate clearly that there is a negative health selection into physically light occupations, introducing a bias (especially in cross-sectional studies) that causes an apparent excess morbidity in occupations with low physical demand.