Patient Global Ratings of Change Did Not Adequately Reflect Change Over Time: A Clinical Cohort Study

BackgroundGlobal ratings of change (GROCs) are commonly used in research and clinical practice to determine which patients respond to therapy, but their validity as a criterion for change has not been firmly established. One factor related to their validity is the length of the recall period.ObjectiveThe study objective was to examine the influence of the length of the recall period on the validity of a GROC for determining true change over time in the clinical setting.DesignThis was a longitudinal, single-cohort observational study.MethodsData from the Focus on Therapeutic Outcomes clinical database were collected for 8,955 patients reporting for physical therapy treatment of a knee disorder. Computerized adaptive testing was used to assess knee functional status (FS) at the initial and final (discharge) physical therapy visits. Each patient's GROC was obtained at discharge. Correlation and linear regression analyses of knee FS and GROC, stratified by length of time between intake and discharge, were conducted.ResultsCorrelations of GROC with knee FS change scores were modest even for the shortest period of recall (0–30 days) and were slightly lower for longer recall periods. Regression analyses using knee FS to predict GROC scores revealed similar findings. Correlations of GROC with intake and discharge scores indicated a strong bias toward discharge status, with little or no influence of baseline status. Standardized regression coefficients fitted the pattern expected for a valid measure of change but confirmed the strong bias toward discharge status.LimitationsOne version of the GROC administered serially in a cohort of patients seen in clinical practice was examined.ConclusionsThese results call into question the validity of GROCs for measuring change over time in routine clinical practice.