The two-factor structure of sleep complaints and its relation to depression and anxiety.

Although sleep complaints are common in depression and anxiety, there is little agreement as to how they should be organized and assessed. It is also unclear whether sleep complaints show specificity with certain disorders or whether they are nonspecific symptoms. The authors examined the structure of sleep complaints and the relations of these complaints to depression and anxiety in 3 samples: college students, older adults, and psychiatric patients. Exploratory and confirmatory factor analyses indicated that sleep complaints consistently defined 2 distinct dimensions: Insomnia and Lassitude. The Insomnia factor included indicators of early, middle, and late insomnia, as well as poor sleep quality. The Lassitude factor included measures of hypersomnia, fatigue, and sleepiness. Both factors were significantly related to symptoms and diagnoses of depression and anxiety. However, Lassitude was more strongly related to symptoms of depression and anxiety than was Insomnia. In addition, Lassitude showed specificity to measures and diagnoses of depression compared with anxiety disorders. This specificity can be explained by Lassitude's relation with negative and positive emotionality, both of which are components of depression.