Composite Pain Index: Reliability, Validity, and Sensitivity of a Patient-Reported Outcome for Research

Abstract

Objective: A single score that represents the multidimensionality of pain would be an innovation for patient-reported outcomes. Our aim was to determine the reliability, validity, and sensitivity of the Composite Pain Index (CPI). Design: Methodological analysis of data from a randomized controlled, pretest/post-test education-based intervention study. Setting: The study was conducted in outpatient oncology clinics. Subjects: The 176 subjects had pain, were 52±12.5 years on average, 63% were female, and 46% had stage IV cancers. Methods: We generated the CPI from pain location, intensity, quality, and pattern scores measured with an electronic version of Melzack's McGill Pain Questionnaire. Results: The internal consistency values for the individual scores comprising the CPI were adequate (0.71 baseline, 0.69 post-test). Principal components analysis extracted one factor with an eigenvalue of 2.17 with explained variance of 54% at baseline and replicated the one factor with an eigenvalue of 2.11 at post-test. The factor loadings for location, intensity, quality, and pattern were 0.65, 0.71, 0.85, and 0.71, respectively (baseline), and 0.59, 0.81, 0.84, and 0.63, respectively (post-test). The CPI was sensitive to an education intervention effect. Conclusions: Findings support the CPI as a score that integrates the multidimensional pain experience in people with cancer. It could be used as a patient-reported outcome measure to quantify the complexity of pain in clinical research and population studies of cancer pain and studied for relevance in other pain populations.