Abstract
BACKGROUND: Sleep disturbance is among the more common complaints reported by chronic pain patients. Because pain-related sleep disturbance may serve as a marker for the assessment of responses to treatment for chronic pain, inclusion of a measure designed to assess the impact of pain on sleep in clinical trial protocols is important, if not necessary. Measures typically used for this purpose lack scales specifically designed for the assessment of the impact of pain on sleep or are based on a single item. Single-item scales lack reliability and, therefore, validity. OBJECTIVES: To investigate the psychometric properties of the five-item Pain and Sleep Questionnaire (PSQ) Index, which is embedded in the eight-item inventory, by applying an accepted methodology using retrospective analyses in controlled clinical trials in which the measure had been administered among patients with chronic nonmalignant pain. METHODS: Data were pooled from nine independent, single-site, double-blind, randomized placebo-controlled clinical trials conducted over a period of approximately 10 years, the majority of which were cross-over designs. A cross-validation approach was adopted with exploratory and confirmatory factor analyses conducted to evaluate the underlying structure and dimensionality of the measure. Internal consistency reliability was evaluated using Cronbach's alpha coefficient. Mean score differences were used to assess the ability of the index to detect important treatment changes. Correlation coefficients were calculated between index scores and scores from other health-related outcome measures to evaluate the criterion validity of the index. Finally, predictive validity was assessed using multiple regression analyses. RESULTS: Pooling the data resulted in a sample of 605 patients (65.5% female; mean age 55.7 years). Findings suggested a revised three-item PSQ Index (PSQ-3). The PSQ-3 demonstrated high internal consistency across samples (ranging from 0.82 to 0.93) and was sensitive to detecting meaningful treatment effects within different chronic pain categories. Moderate to strong correlations (r>0.40) between the PSQ-3 and other health-related outcome measures provided preliminary evidence for criterion-related validity. Results of multiple regression analyses demonstrated that the PSQ-3 accounted for between 29% and 40% of the variance in scores from other health-related outcome measures. CONCLUSIONS: Results support the scoring of a revised three-item index for the assessment of the impact of pain on sleep. The revised index demonstrated acceptable levels of internal consistency and preliminary support for the structural, criterion-related and predictive validity of the index was achieved.