Measurement properties of the Medical Outcomes Study Sleep Scale in patients with fibromyalgia

ObjectiveSleep problems are a common symptom of fibromyalgia (FM). The objective of this study was to evaluate the Medical Outcomes Study (MOS) Sleep Scale as a measure of FM-related sleep problems.MethodsAnalyses were based on data from the 1056 and 1077 studies, two randomized, double-blind, placebo-controlled trials of pregabalin for adults with FM. MOS Sleep Scale scores of study patients were compared with United States normative scores using a one-sample Z test. Subscale structure of the MOS was evaluated by confirmatory factor analyses, internal consistency was evaluated using Cronbach’s alpha reliability coefficients. Estimated clinically important differences (CID) in MOS Sleep Disturbance subscale scores were evaluated using mixed-effects models of change in subscale scores as a function of the Patient Global Impression of Change (PGIC).Results1056 and 1077 included 748 and 745 patients, respectively. Most patients were female (1056: 94.4%, 1077: 94.5%) and white (1056: 90.2%, 1077: 91.0%). Mean ages were 48.8 years (1056) and 50.1 years (1077). Baseline MOS Sleep Scale scores were statistically (P < 0.001) and substantially poorer than general population values. The MOS subscale structure was confirmed in both studies at each assessment except at baseline in the 1056 study. Cronbach’s alpha coefficients were acceptable, at least 0.70, for all multi-item scales at baseline and end-of-study assessments in both studies, with the exception of the Sleep Adequacy subscale at baseline. The estimated CID for the MOS Sleep Disturbance subscale was 7.9.ConclusionsThe MOS Sleep Scale is an appropriate measure of FM-related sleep problems. These analyses provide the foundation for further use and evaluation of the MOS Sleep Scale in FM patients.