Evaluating the measurement properties of the 26-item Expanded Prostate Cancer Index Composite (EPIC-26) with a multicenter cohort

Abstract

Introduction: We aimed to evaluate the psychometric properties of the 26-item Expanded Prostate Cancer Index Composite (EPIC-26) for measuring the quality of life in patients treated for localized prostate cancer. The EPIC-26 is a patient-reported outcome instrument recommended for use with patients treated for localized prostate cancer. Methods: This study is based on data collected prospectively between September 2014 and February 2017 in Alberta, Canada. Men were treated with either radical prostatectomy or radiation therapy and administered the EPIC-26. Responses to the EPIC-26 were the primary outcome. Construct validity was measured using confirmatory factor analysis. Reliability was measured using Chronbach’s alpha and item-total correlation. Ceiling and floor effects were also investigated. Results: EPIC-26 response data from 205 participants (prostatectomy =138; radiation=60; both=7) were used in this analysis. The EPIC-26 was administered an average of 33.8 weeks after treatment. The confirmatory factor analysis model did not meet the threshold for adequate fit. Several items had near-zero factor loadings and were non-significant. Four out of the EPIC- 26’s five domains met the acceptable reliability threshold based on Cronbach’s alpha. Ceiling effects were observed in four out of five domains. Conclusions: The EPIC-26 demonstrated poor construct validity, adequate reliability, and large ceiling effects. Several issues were observed, suggesting that the instrument’s five domains were not well-defined by their respective items. The original EPIC’s conceptual framework should be reviewed and the shortened instrument revised to improve its performance for measuring post-treatment quality of life.