Linguistic and cross – cultural adaptation of the Lithuanian version of Insomnia Severity Index

¹Miglė Šostakaitė-Babenskienė, ¹Živilė Vaičekauskytė, ¹Evelina Pajėdienė,

¹Department of Neurology, Kaunas Clinics, Hospital of Lithuanian University of Health Sciences, Kaunas, Lithuania.


Background:the Insomnia Severity Index (ISI) has been developed to assess the severity of the disorder, and has been shown to be a reliable and valid instrument to detect patients with insomnia.  Lithuanian version of ISI (ISI – L) would facilitate insomnia diagnostics.

Aim: to adapt the Lithuanian version of Insomnia Severity Index and evaluate its psychometric properties.

Materials and methods: 324 adults from general population at age 18 to 64 who fulfilled the inclusion criteria and signed the informed consent participated in the study. All subjects completed the questionnaires that included sociodemographic information, Pittsburgh sleep quality index (PSQI), Hospital Anxiety and Depression Scale (HADS) and the Epworth sleepiness scale (ESS). The reliability of the questionnaire was examined by calculating its internal consistency with Cronbach‘s α (statistically significant when Cronbach’s α > 0.7).

Results: high internal consistency coefficients were obtained for the ISI (Cronbach α = 0.863). Subthreshold severity insomnia could be suspected for 99 participants (30.6%). Subthreshold severity insomnia could be suspected for 99 participants (30.6%). Moderate severity insomnia – for 34 participants (10.5%). Severe insomnia – for 4 participants (1.2%). Total mean ISI score for all participants was 7.32 (SD 5.369, median 6).  Significant correlation of ISI scores and PSQI (p< 0.005), with HADS anxiety, with HADS depression was detected.

Conclusions: according to the adjusted ISI – L, insomnia could be suspected for nearly half of participants.

High internal consistency of the ISI – L showed that this scale is reliable and can be adapted for the use in Lithuania.

Keywords: Insomnia, Insomnia Severity Index, validisation, adaptation.