Psychometric properties of a sleep questionnaire for use in individuals with intellectual disabilities

► Sleep questionnaire reliable tool to assess sleep in intellectual disability (ID). ► Snoring and sleep apnea are two different factors in individuals with ID. ► Sleep questionnaire discriminates clients referred to sleep clinic from controls. We examined the psychometric properties of one part of the Sleep Questionnaire developed by Simonds and Parraga (SQ–SP; 1982), a questionnaire that is frequently used to explore sleep problems and behaviors related to sleep in individuals with intellectual disability (ID). The SQ–SP was completed for 345 individuals with ID (sleep clinic n = 146; control group n = 103; published studies n = 68; psychiatric clinic n = 28). Internal consistency was good (Cronbach's α = .80) and test–retest reliability for the total SQ–SP score was also good (Spearman's rank correlation = .83, p < .01). Convergent validity was adequate ( r = .79, p < .001) and concurrent validity was satisfactory ( r = .52, p < .001). Exploratory factor analysis suggested a 5-factor structure (Snoring, Daytime sleepiness, Complaints related to sleep, Sleep apnea and Anxiety related to sleep). Internal consistency of the five factors ranged from modest (Cronbach's α = .57) to good (Cronbach's α = .82). Confirmatory factor analysis corroborated the 5-factor structure. The Composite Sleep Index, the total SQ–SP score and the factor scores on Daytime Sleepiness and Complaints related to sleep were able to differentiate the control group from the sleep clinic group. The SQ–SP appears to be a reliable and valid tool in assessing sleep and different types of sleep disturbance in individuals with ID.