Reliability of a scale assessing depressed mood in the context of sleep

The current study assessed the reliability of Kandel & Davies (1982) mood scale with and without sleep-related items. Brown University first-year students (mean age = 18.1 years; 108 females) completed online biweekly surveys after weeks 2, 6, 8, and 10 and on two consecutive days after weeks 4 and 12 of their first semester. One hundred seventy-eight students completed at least two biweekly online surveys with 128 students completing all six surveys. The scale was examined as a 1) full 6-item scale, 2) 5-item scale excluding the sleep item, and 3) 4-item scale excluding the sleep and tired items. Intraclass correlations (ICC) values for consecutive-day assessments and six biweekly surveys were similar and not a function of the weeks evaluated. Total-item correlations and inter-measure correlations with the Center for Epidemiologic Studies - Depressed Mood Scale (CES-D) supported the removal of the sleep-related items from the 6-item scale. These analyses confirm the reliability of the original Kandel and Davies depressed mood scale as well as without the sleep-related items.