Validity of 2 sleep quality items to be used in a large cohort study of kidney transplant recipients

Context-Poor sleep quality and poor daytime functioning affect many kidney transplant patients. Objective-To evaluate the validity of 2 items assessing sleep quality and daytime functioning using the Pittsburgh Sleep Quality Index as reference standard before use in a large cohort study, following the American Psychological Association's guidelines. Design-A cross-sectional study using a psychosocial questionnaire developed for a large cohort study and the Pittsburgh Sleep Quality Index. Sample and Setting-One hundred thirty-five home-dwelling kidney transplant patients aged 21 to 76 years (mean, 51.6 years; SD, 11.9 years). Main Outcome Measures-Evidence on content, internal structure, and relation to other variables. Results-The Pittsburgh Sleep Quality Index indicated a 47.4% prevalence of poor sleep quality; the sleep quality item in the psychosocial questionnaire showed a 30.7% prevalence of poor sleep quality and a 34.1% prevalence of poor daytime functioning. Content validity was good for the psychosocial questionnaire's sleep quality item but poor for its daytime functioning item. As hypothesized, the psychosocial questionnaire's sleep quality item was moderately correlated with its daytime functioning item (Spearman rho, rho(s)=0.520, P<.001), indicating related but distinct concepts. When combined, the 2 items from the psychosocial questionnaire showed significant correlations with the total score on the Pittsburgh Sleep Quality Index (rho(s)=-0.784, P<.001), depressive symptoms (rho(s)=-0.680, P<.001), perceived health status (rho(s)=0.619, P<.001), and subjective health status (rho(s)=0.671, P<.001) in the expected directions. Conclusion-For kidney transplant patients, validity is strong for the psychosocial questionnaire's sleep quality item, but the mixed findings regarding the validity of the daytime functioning item suggest that additional items are needed to measure daytime functioning. (Progress in Transplantation. 2011;21:27-35)