Psychometric properties of the Insomnia Severity Index in a sample of family dementia caregivers

Study objectives Family caregivers of people with dementia frequently report sleep problems that are linked to depressive and anxious symptoms. However, data are needed regarding the psychometric properties of specific measures of sleep problems in caregiving populations. The aim of this study is to analyse the psychometric properties of the Insomnia Severity Index (ISI; Morin, 1993) in a Spanish dementia caregiver sample. Methods 271 participants took part in face-to face interviews where, along with sociodemographic variables, caregivers' sleep problems, depressive and anxious symptoms were measured. The psychometric properties of the ISI were analysed through Confirmatory Factor Analysis (CFA) and analysis of the internal consistency and convergent and criterion validity. Results The Spanish version of the Insomnia Severity Index showed adequate indices of internal consistency (Cronbach's alpha = 0.78) in our sample of family caregivers of people with dementia. A one-factor structure provided a better fit to the data than two- and three-factor structures. The ISI was significantly associated with lower sleep quality, less average sleep time per day and lower self-perception of vitality, as well as with higher depressive and anxious symptoms. Differences in ISI scores were found between people with and without depressive and anxious symptoms. Statistically significant gender-based differences in sleep problems were also found, with female caregivers showing higher sleep problems. Conclusions The ISI is a reliable and valid instrument to assess the subjective severity of sleep problems in the family dementia caregiver population and may be a useful instrument in intervention and research settings. Additional evidence was also provided of the importance of considering sleep problems in the studied population.