Send to

Choose Destination
Sleep Med. 2015 May;16(5):598-603. doi: 10.1016/j.sleep.2014.11.016. Epub 2015 Feb 12.

Validating the cross-cultural factor structure and invariance property of the Insomnia Severity Index: evidence based on ordinal EFA and CFA.

Author information

Department of Psychology, University of Kansas, 1415 Jayhawk Blvd, Fraser Hall, Room 426, Lawrence, KS 66045-7556, USA; Center of Research Method and Data Analysis, University of Kansas, 1415 Jayhawk Blvd, Waston Library 470, Lawrence, KS, USA.
Department of Psychology/The Research Center for Mind, Brain, & Learning, National Chengchi University, No. 64, Sec 2, ZhiNan Rd., Wenshan District, Taipei, Taiwan. Electronic address:
École de Psychologie, Université Laval, Québec, QC, Canada; Centre de Recherche de l'Institut Universitaire en Santé Mentale de Québec, Québec, QC, Canada.



The purpose of this study is to examine the factor structure of the Insomnia Severity Index (ISI) across samples recruited from different countries. We tried to identify the most appropriate factor model for the ISI and further examined the measurement invariance property of the ISI across samples from different countries.


Our analyses included one data set collected from a Taiwanese sample and two data sets obtained from samples in Hong Kong and Canada. The data set collected in Taiwan was analyzed with ordinal exploratory factor analysis (EFA) to obtain the appropriate factor model for the ISI. After that, we conducted a series of confirmatory factor analyses (CFAs), which is a special case of the structural equation model (SEM) that concerns the parameters in the measurement model, to the statistics collected in Canada and Hong Kong. The purposes of these CFA were to cross-validate the result obtained from EFA and further examine the cross-cultural measurement invariance of the ISI.


The three-factor model outperforms other models in terms of global fit indices in Taiwan's population. Its external validity is also supported by confirmatory factor analyses. Furthermore, the measurement invariance analyses show that the strong invariance property between the samples from different cultures holds, providing evidence that the ISI results obtained in different cultures are comparable.


The factorial validity of the ISI is stable in different populations. More importantly, its invariance property across cultures suggests that the ISI is a valid measure of the insomnia severity construct across countries.


Factorial structure; Insomnia Severity Index; Measurement invariance; Multigroup structural equation model; Ordinal exploratory factor analysis

[Indexed for MEDLINE]

Supplemental Content

Full text links

Icon for Elsevier Science
Loading ...
Support Center