Evaluation of the reliability and validity of the Medical Outcomes Study sleep scale in patients with painful diabetic peripheral neuropathy during an international clinical trial

BACKGROUND: Sleep is an important element of functioning and well-being. The Medical Outcomes Study Sleep Scale (MOS-Sleep) includes 12 items assessing sleep disturbance, sleep adequacy, somnolence, quantity of sleep, snoring, and awakening short of breath or with a headache. A sleep problems index, grouping items from each of the former domains, is also available. This study evaluates the psychometric properties of MOS-Sleep Scale in a painful diabetic peripheral neuropathic population based on a clinical trial conducted in six countries. METHODS: Clinical data and health-related quality of life data were collected at baseline and after 12 weeks of follow-up. Overall, 396 patients were included in the analysis. Psychometric properties of the MOS-Sleep were assessed in the overall population and per country when the sample size was sufficient. Internal consistency reliability was assessed by Cronbach's alpha; the structure of the instrument was assessed by verifying item convergent and discriminant criteria; construct validity was evaluated by examining the relationships between MOS-Sleep scores and sleep interference and pain scores, and SF-36 scores; effect-sizes were used to assess the MOS-Sleep responsiveness. The study was conducted in compliance with United States Food and Drug Administration regulations for informed consent and protection of patient rights. RESULTS: Cronbach's alpha ranged from 0.71 to 0.81 for the multi-item dimensions and the sleep problems index. Item convergent and discriminant criteria were satisfied with item-scale correlations for hypothesized dimensions higher than 0.40 and tending to exceed the correlations of items with other dimensions, respectively. Taken individually, German, Polish and English language versions had good internal consistency reliability and dimension structure. Construct validity was supported with lower sleep adequacy score and greater sleep problems index scores associated with measures of sleep interference and pain scores. In addition, correlations between the SF-36 scores and the MOS-Sleep scores were low to moderate, ranging from -0.28 to -0.53. Responsiveness was supported by effect sizes > 0.80 for patients who improved according to the mean sleep interference and pain scores and clinician and patient global impression of change (p < 0.0001). CONCLUSION: The MOS-Sleep had good psychometric properties in this painful diabetic peripheral neuropathic population. TRIAL REGISTRATION: As this study was conducted from 2000 to 2002 (i.e., before the filing requirement came out), no trial registration number is available.