Insomnia Severity Index: A reliability generalisation meta-analysis

The aim of the current study was to conduct a reliability generalisation (RG) meta-analysis of Cronbach's alpha for the Insomnia Severity Index (ISI). A systematic search of three databases (PubMed, Scopus, and Web of Science) from inception to 12 March 2021 was performed. Publications that reported Cronbach's alpha for the total ISI score were included. Only psychometric-focussed studies were considered. Meta-analysis was carried out using a random-effects model to derive a pooled estimate of Cronbach's alphas. The number of participants in the included publications ranged from 25 to 12,056, with 33 studies (42 estimates) comprising internal consistency coefficients, and a combined sample size of N = 29,688. The age range of the included publications was from 13.4 to 74.3 years. Data extraction implied 33 publications out of 706 found through the database search. Cronbach's alphas ranged from 0.65 to 0.92. The majority of the reported coefficients were ≥0.7 and presented a low risk of bias (n = 32). The pooled alpha coefficient was 0.83 (IC [0.81-0.85]; SE = 0.009) with high heterogeneity among the included publications (I²  = 97%). Subgroup analyses including moderators such as continent, setting, risk of bias, and age did not affect significantly the overall result. In general, the cumulative estimate of Cronbach's alpha for the ISI is good. However, this finding should be interpreted with caution since there is a high heterogeneity level and some of the studies might not have checked the assumptions underlying Cronbach's alphas.