Self-reported sleep and short sleep duration (primary predictor).
Phenotypes of self-reported short sleep were defined by utilizing questions from The Pittsburgh Sleep Quality Index (PSQI), which measures sleep quality and quantity over the previous month. Individual questions were used to operationalize phenotypes of habitual short sleep duration. Sleep duration was assessed via the question, “during the past month, how many hours of actual sleep did you get a night?” Short sleep was defined as self-reported sleep duration of < 7 hours per night. Questions about sleep onset latency (SOL), wake after sleep onset (WASO), and sleep efficiency (SE) were also utilized to examine short sleepers with an additional sleep disturbance. Short sleepers with a prolonged SOL were defined as individuals who reported a SOL ≥ 30 minutes. Short sleepers with a WASO impairment were defined as individuals who reported waking up late at night or early in the morning at least three times a week. Short sleepers with poor SE were defined by a SE < 85% which was calculated from the PSQI as the ratio of total sleep time compared to total time spent in bed. These classifications were not mutually exclusive and were defined as additional sleep disturbances among short sleepers.