Job demands, job control, and mental health in an 11-year follow-up study: Normal and reversed relationships

Despite numerous studies of the demand-control model, there is a need for more longitudinal studies to test not only the normal, but also the reversed and reciprocal relationships between work characteristics and mental health. There is also a need for more studies of the multiplicative interaction between demands and control with respect to mental health, which is different from the simple additive effect of the two variables. This is a longitudinal study with an exceptionally long period of follow-up (11 years), with the focus on normal as well as reciprocal and reversed causality between work characteristics and mental health, as measured by reliable instruments close to the original definitions of Karasek. The study was based on a sample of 439 Norwegian employees of different occupations who had stayed in the same profession during the follow-up period. The results were in agreement with the hypothesis that low job control, and in particular low control in combination with high demands ("high strain jobs"), has a negative effect on mental health. There was a significant multiplicative interaction between demands and control, indicating a "buffering" effect of job control. Job demands alone were not significantly associated with mental health. The reversed relationship hypothesis was supported for job demands, but not for job control.