METHODS: Data are from four 12-week multicenter, double-blinded, randomized, placebo-controlled clinical trials (total N=2,674 patients) for once-daily tramadol extended-release (ER) tablets in treating chronic osteoarthritis pain and low back pain. The trials assessed the efficacy of tramadol ER in reducing pain leading to sleep improvement, which was measured by the CPSI. The five items of the CPSI included trouble falling asleep, needing sleep medication, awakenings due to pain in the night and morning, and overall quality of sleep (CPSI 1, 2, 3, 4, and 5, respectively). Exploratory and confirmatory factor analyses were conducted to evaluate the underlying structure of the CPSI. Known-groups validity method was used to test the discriminant validity of the CPSI. Analysis of variance was used to test the significance of the differences in mean CPSI scores.

RESULTS: Results from exploratory and confirmatory factor analyses revealed that a single sleep problems index could be scored from three of the CPSI items (CPSI 1, 3, and 4). All three items share the attribution of sleep problems related to pain and had high loadings (>0.80) on the single factor. All CPSI scales significantly (p<0.001) discriminated between groups of patients that differed in the presence and severity of sleep problems at baseline and over time in the hypothesized manner. The CPSI sleep index showed the best discriminant validity (highest F-statistic) in all known-groups validity tests.

CONCLUSIONS: This study provides preliminary psychometric evidence to support the scoring of a single sleep problems index from three of the five CPSI items. The CPSI sleep problems index was highly reliable and demonstrated stronger discriminant validity than each of the individual CPSI items in known groups-validity tests.