External validation of psychological job demands in a bus driver sample.

Psychosocial risk factors have been considered as characteristics of the work environment rather than an individual issue, but their presence in the workplace is usually measured by self-reported questionnaires, based on worker attitudes. The objective of the study was to compare a self-reported measure of psychological job demands in a bus driver sample with selected indicators of bus company activity, as external 'objective' indicators, in order to assess its external validity. The final sample included 713 drivers in 41 routes. Self-reported measures of psychosocial work risk factors were obtained by the Job Content Questionnaire (JCQ). Four external indicators were available for each route: passengers, break times, bus incidents, and regulating actions. Spearman's correlation coefficient was estimated to assess the validity. Correlation coefficients showed that self-reported psychological demands were statistically significant correlated (p<0.05) with two external indicators: bus incidents (rho=0.397), and regulating actions (rho=0.475). Self-reported psychosocial risk factors have been compared with independent external indicators of the psychosocial work environment, trying to avoid any subject's perception. According to our results, psychological demands measured by the JCQ seem to reflect the actual psychosocial work environment. Other studies are necessary to confirm these results and to assess job control and job social support. This would be another step in improving our knowledge of the quality of measurement of psychosocial risk factors.