Towards a more comprehensive definition of shift work tolerance.

The aim of the present study was to define the nature of individual differences in shift work tolerance (SWT). This was investigated by an exploratory factor analysis of scores from a wide range of established instruments designed to measure sleep, sleepiness, fatigue, social functioning, as well as physical and mental health. Data were collected from a representative sample of 1,529 Norwegian nurses engaged in rotating shift work. The analyses yielded two factors that seemed to be especially relevant for SWT, namely "Well-being" and "Physical health". Both factors were related to several demographic and personality variables. In addition, both factors were related to job satisfaction, social support and negative acts, while Well-being was also related to coping. These results support the construct and concurrent validity of the Well-being and Physical factors of SWT. Our findings represent a step towards answering calls from previous research concerning the establishment of a wider definition of individual differences in SWT.