title: Validity and reliability of the Iranian version of the insomnia severity index.
abstract: BACKGROUND
  The Insomnia Severity Index (ISI) is a short subjective questionnaire which helps physicians in making decisions about patients suffering from insomnia. The present study was an attempt to test the reliability and validity of the Iranian version of the ISI and to measure the correlation between ISI items and polysomnography results in chronic insomnia patients.
  
  
  METHODS
  Two groups responded to the Persian translation of four questionnaires; ISI, Pittsburg Sleep Quality Index (PSQI), Epworth Sleepiness Scale (ESS), and General Health Questionnaire (GHQ). The first group consisted of 135 patients diagnosed with chronic insomnia, and the second group was comprised of 55 normal people. After completing the questionnaires, the insomniac patients underwent standard overnight polysomnography.
  
  
  RESULTS
  The internal consistency demonstrated by Cronbach's alpha coefficient was above 0.8 for both groups. The Intra-class correlation coefficient was above 0.7 after two weeks for both groups. The correlations between ISI, PSQI, ESS, and GHQ were high. In addition, close correlations were found between scores obtained from the ISI questionnaire items in insomniac patients with corresponding polysomnographic variables.
  
  
  CONCLUSIONS
  The Iranian version of the ISI is a reliable and valid instrument. It is a valuable short and first-line questionnaire for insomnia research and clinical work.
authors.affiliation: Qazvin University of Medical Sciences, Qazvin, Iran.
authors.forename: Zohreh
authors.initials: Z
authors.lastname: Yazdi
authors.forename: Khosro
authors.initials: K
authors.lastname: Sadeghniiat-Haghighi
authors.forename: Mohammad Ali
authors.initials: MA
authors.lastname: Zohal
authors.forename: Khadijeh
authors.initials: K
authors.lastname: Elmizadeh
keywords: Insomnia Severity Index; Iran; insomnia; reliability; validity