A validation of the revised circadian type inventory in a working sample

The measurement properties and construct validity of the two-factor 11-item Circadian Type Inventory (CTI) was examined in a working sample comprising shiftworkers and day workers. The two factors explained 50.04% of the variance (LV = 20.24% and FR = 29.80%). Inter-item correlations were all significant and the item-total correlations suggested the weakness of one item in the LV scale. Cronbach's alpha was 0.72 (LV) and 0.79 (FR). Confirmatory factor analysis however provided marginal support for the posited structure. Vigorous types were significantly more alert than languid types across the day and suggested they are less influenced by sleep inertia on waking. Vigorous types also reported needing significantly less sleep. Significant differences in alertness between flexible and rigid types were found between 16:00 and 22:00 and suggested flexible types are less influenced by circadian and wakefulness factors during these periods. Flexible types also reported significantly less sleep need compared to rigid types. The findings suggested vigorous and flexible types would best cope with shiftwork. It is concluded that the CTI demonstrated good reliability and validity in a working sample. Recommendations for future studies are made.