Factor structure assessment of the Insomnia Severity Index among Korean middle-aged adults

ObjectivesInsomnia is highly prevalent among middle-aged adults. The Insomnia Severity Index (ISI) is a commonly used assessment tool for perceived severity of insomnia in clinical and research settings. Studies have shown that the ISI is theoretically sound and demonstrates strong psychometric properties in both adult samples of clinical patients and student samples. Despite these findings, some concerns persist regarding the instrument's validity of application. To determine the psychometric properties of the ISI, this study examined its underlying factor structure using a confirmatory factor analysis (CFA) framework with a sample of Korean middle-aged adults.MethodsA total of 501 participants aged between 40 and 64 (M = 50.9, SD = 6.00) completed the Korean version of the ISI. The data were subjected to CFA to examine the factor structure and compare the goodness-of-fit of the tool's previously proposed models. Internal consistency of the ISI was assessed using Cronbach's alpha and McDonald's omega.ResultsA one-factor model demonstrated superior fit to the data (chi 2 = 27.6, df = 9; chi 2/df = 3.0; CFI =.98; TLI =.97; RMSEA =.052 (90% CI =.036-.082); SRMR =.024), compared to two- and three-factor models. The ISI showed adequate internal consistency (alpha = .81, omega = .81).ConclusionThe ISI is a valid and reliable measure of subjective severity of insomnia in Korean-speaking populations. Its one-factor structure makes it psychometrically robust and feasible for clinical practice.