Development and validation of the Hypersomnia Severity Index (HSI): A measure to assess hypersomnia severity and impairment in psychiatric disorders

Hypersomnia is common in psychiatric disorders, yet there are few self-report measures that adequately characterize this sleep disturbance. The objective of this study was to validate the Hypersomnia Severity Index (HSI), a tool designed to measure severity, distress and impairment of hypersomnia in psychiatric populations. Psychometric properties were evaluated in an undergraduate Scale Development sample (N = 381) and two psychiatric Scale Validation samples: euthymic bipolar participants with a range of sleep complaints (N = 89), and unmedicated unipolar depressed participants (N = 21) meeting operational criteria for hypersomnolence disorder. Exploratory factor analysis and confirmatory factor analysis in the Scale Development and Validation samples, respectively, suggested a two-factor structure representing Hypersomnia Symptoms and Distress/Impairment best fit the data. Convergent validity was established by significant associations with the Epworth Sleepiness Scale (ESS), Pittsburgh Sleep Quality Index (PSQI), and the Sheehan Disability Scale in both samples. Construct validity was further supported by significant correlations between the Scale Validation sample and two weeks of diary- and actigraphy-determined total sleep time and time in bed. A cutoff score of 10 maximally discriminated between those with hypersomnia and those without. The HSI shows promise as a measure of hypersomnia that is commonly seen in psychiatric disorders, and may be of use to both researchers and clinicians.