Test‐retest Reliability of the Pittsburgh Sleep Quality Index in Nursing Home Residents

To the Editor: Sleep problems in the nursing home are common1 but difficult to measure. A variety of instruments are available for evaluating sleep, but none are without their limitations in the nursing home setting. Objective measures, such as polysomnography, actigraphy, and systematic observations, are cumbersome and expensive. In addition, although these measures provide information on sleep parameters (e.g., sleep latency, duration, efficiency) they cannot precisely define qualitative aspects of sleep (e.g., restfulness and satisfaction).2,3 Subjective instruments, such as sleep questionnaires (self-administered) and interviews attempt to measure both quantitative and qualitative aspects of sleep. These tools also offer the advantage of low cost and low respondent burden. Although sleep fragmentation in the nursing home has been well documented using objective measures,4,5 a sleep questionnaire has not been designed and validated specifically for nursing home use. The Pittsburgh Sleep Quality Index (PSQI)2 is an instrument that has been validated in middle-aged outpatients. It was originally designed as a self-administered questionnaire to assess sleep quality over a 1-month interval. Nineteen questions generate seven “component scores,” the sum of which gives a global score that facilitates comparison between subjects. The purpose of our study was to determine the test-retest reliability of the PSQI in nursing home residents. The subjects were 19 cognitively intact residents of the Extended Care and Rehabilitation Center of the Durham Veteran Affairs Medical Center (VAMC). The PSQI was adapted for use in interview format inasmuch as we predicted that many nursing home residents would be too frail to complete the questionnaire by themselves. Most questions were simplified using a branching technique. Example Original Question: 5i) During the past month, how often have you had trouble sleeping because you had bad dreams? . Not during the past month ____ . Less then once a week ____ . Once or twice a week ____ . Three or more times a week ____ Interview format: 5i) During the past month, have you had trouble sleeping because you had bad dreams? The same interviewer (AG) administered the PSQI on two occasions, an average of 19 days apart (range 3-44). Test-retest reliability was calculated using intraclass correlations (ICC)6 for both component and global scores. One subject answered “I don't know” to five questions and, therefore, was excluded from the analysis. Of the remaining 18 subjects 17 were male and the mean age was 75 years. The ICC of each component was good (.4 ≤ ICC ≤ .75) to excellent (ICC > .75),7 ranging from 0.45 (component “daytime dysfunction”) to 0.84 (component “use of sleeping medications”). The ICC of the global score was excellent (ICC = 0.82, Table 1). The PSQI, when administered in an interview format to cognitively intact nursing home residents, demonstrated good test-retest reliability. We used an interview format because it offers the advantage of minimizing missing and inappropriate responses.7 In our study, 18 of 19 residents were able to successfully complete the instrument, allowing calculation of a global score. This is an essential part of the PSQI because it is this global score that differentiates good from poor sleepers. Because all of our subjects were cognitively intact, our results cannot be generalized to all nursing home residents. Even though the interview-administered PSQI does not provide a specific diagnosis, its discriminative ability makes it an attractive research instrument as well as a clinical screening tool to identify older subjects who have poor sleep quality and need further evaluation. Clinicians and investigators might consider expanding its use to older people in other settings. It could be useful, for example, in outpatient clinics and assisted living situations for those subjects who are cognitively intact but too frail to self-administer a questionnaire.