An intra‐individual test of the demands‐control model: A weekly diary study of psychological strain in portfolio workers

Twenty‐five years of research on Karasek's job strain model has produced evidence that jobs involving high demands, low control and low social support may produce psychological strain. The present study takes this research in a new direction by using a time‐sampling methodology with a group of portfolio workers (self‐employed individuals who work for multiple clients) to examine whether working weeks that involve more of these characteristics are associated with greater psychological strain. The study also examines whether workers' optimism moderates the intra‐individual relationship between job characteristics and strain. Every week for 26 weeks, 65 portfolio workers completed a diary containing measures of work demands, job control, social support and strain. Multi‐level analyses supported the additive but not the interactive form of the job strain model. However, differences in portfolio workers' optimism moderated an interactive effect of weekly demands and control on anxiety and depression, such that the highest levels of strain were experienced by pessimists under conditions of low control and high demands. The results suggest that psychological strain can vary with temporal variations in job characteristics and that a person‐situation approach is appropriate for understanding these dynamics.