Influence of locus of control on mood state disturbance after short-term sleep deprivation.

Twenty-eight healthy university students were classified as having either an internal (n = 14) or external (n = 14) locus of control. Before and after 26-30 hours of sleep deprivation, their mood state was evaluated using the Profile of Mood States questionnaire. There was a significant sleep status x locus of control interaction effect on mood state disturbance (p = 0.049). In the individuals with an external locus of control, there was an increase (p < 0.001) in total mood disturbance from (mean +/- standard deviation) 115 +/- 23 during baseline testing to 148 +/- 22 after sleep loss (effect size = 1.4). Sleep loss did not significantly affect total mood disturbance in the subjects with an internal locus of control (115 +/- 26 vs. 128 +/- 34). These results suggest that locus of control is a factor that influences the degree of mood state disturbance caused by short-term sleep deprivation.