BACKGROUND: Global 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.OBJECTIVE: The 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.DESIGN: This was a longitudinal, single-cohort observational study.METHODS: Data 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.RESULTS: Correlations 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.LIMITATIONS: One version of the GROC administered serially in a cohort of patients seen in clinical practice was examined.CONCLUSIONS: These results call into question the validity of GROCs for measuring change over time in routine clinical practice.
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