Factor Analysis of Sleep-Wake Traits.

Factor loadings (Statistica, StatSoft, Inc.) of the 20 sleep-wake variables in the 24-hr period are shown with the factor-determining loading values bolded (generally greater than ��0.75). The 5 factors account for 81 percent of the total variance in the data. See Supporting Information for complete trait descriptions, and Supporting Information Table S2 for a 1000�� bootstrap-obtained estimate of the 95% confidence intervals of the factor loading values.