SELECTION RELATED TO MUSCULOSKELETAL COMPLAINTS AMONG EMPLOYEES

Objectives-To (a) describe differences in the outcome of cross section al and longitudinal analysis on musculoskeletal complaints relative to age and work demands, and (b) to assess the entrance and drop out sel ection on musculoskeletal complaints among groups of employees relativ e to age and work demands. Methods-A study population was selected on the basis of questionnaire data from periodical occupational health su rveys of almost 45 000 employees collected between 1982 and 1993, From all companies within this data base that participated twice in compan y wide surveys four years apart, male employees were selected, and str atified far age and work demands. There were several populations: foll ow up (participation in both surveys); drop out (participation only in the first: survey); entrance (participation only at the second survey ); and two cross sectional populations (all participants at each surve y). Prevalences of back complaints and turnover rates were analysed. R esults-Reported back complaints in the cross sectional analysis declin ed over the oldest age groups in heavy physical work versus a small in crease in the longitudinal analysis. The age group 50-9 and back compl aints were identified as predictors at the first survey for nob partic ipating at the second survey. Neither age nor work demands at the firs t survey indicated drop out among those employees with back complaints at the first survey. The effects of entrance selection on estimated p revalences were small. Conclusions-The results indicate that musculosk eletal disorders lead to selection out of work, affecting the validity of both cross sectional and longitudinal epidemiological studies. In future studies analyses of turnover figures on musculoskeletal complai nts relative to work demands and age are recommended.