Scale reliability and validity of the Karasek 'Job Demand-Control-Support' model in the Belstress study

In studies of occupational stress, a leading theoretical model is the `Job Demand-Control-Support' model (Karasek, and Theorell, 1990). This states that the most adverse job-related strain reactions are to be expected in jobs characterized by high job demands, low control and low worksite support. The reliability and validity of the scales was evaluated in a sample of 21,419 employees out of 25 large companies across Belgium. Participants completed items from the job Content Questionnaire (Karasek, 1985) in either French or Dutch translation. Data were handled by a French-speaking and a Dutch-speaking centre, respectively. Occupational groups were identified according to the International Standard of Classification, ISCO. Basically, the data support the assumptions of the model. The internal consistency was adequate: Cronbach's alpha varied between .77 and .83 for Psychological demands (9-item version), Decision latitude, Supervisor social support and Co-worker social support. These four common factors were clearly distinguished in a factor analysis. A confirmatory factor analysis pointed to the correlation among these factors and illustrated similar loading structures within subgroups according to age, gender and education. Lower occupational grades tended to display lower mean values of psychological demands and decision latitude than those observed in higher grades. Blue collar workers, at least in men, were found to be less exposed to high strain working conditions (high demands-low control) than clerks and service workers. 'Feeling stressed' was found to be more strongly associated with psychological demands than with decision latitude or social support; the reverse held true for `job satisfaction'.