Validity and reliability of the Persian version of the Insomnia Diurnal Impact Scale (IDIS)

Background Insomnia disorder is characterized by nighttime and daytime symptoms. The aim of this study was to assess the validity and reliability of a Persian version of the Insomnia Diurnal Impact Scale (IDIS) as a screening tool to evaluate diurnal effects of sleep fragmentation in Iranians. Methods Of 300 individuals recruited, 150 had insomnia disorder based on DSM-5 criteria and 150 were good sleepers based on research diagnostic criteria. All subjects completed the IDIS, Pittsburg Sleep Quality Index, Insomnia Severity Index, Depression-Anxiety-Stress Scale-21, and sleep diaries. Results The Persian version of the IDIS showed adequate psychometric properties for internal consistency and test-retest reliability. The result of principal component analysis confirmed a single component with six items as the final structure of the scale in the insomniac group. The total IDIS score significantly correlated with the Pittsburg Sleep Quality Index, Insomnia Severity Index, and subscales of Depression-Anxiety-Stress Scale-21 verifying the convergent validity of the scale. The Persian version of the IDIS significantly discriminated the insomniac group from the non-insomniac group. The result of the fit estimates for the one-factor unidimensional model met the previously specified fit criteria and adequately fit the data in the non-insomniac group. Conclusion The Persian version of the IDIS was shown to be a valid and reliable clinical tool in evaluating the daytime consequences of insomnia in Iranians.