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Reliable Change (RC) indices are a group of statistical techniques used in many areas of medicine to help to determine when an individual’s performance on a neuropsychological test has changed from a previous assessment1 with the same test. Recently, in sports concussion, numerous authors have advocated the application of RC analyses to neuropsychological test data collected at baseline (preseason) and after a concussion.2,3 These authors have stated that the results of RC analyses provide the best means for guiding decisions about whether or not true change in cognitive function has occurred after a concussion, and can therefore assist the return to play decision making process. Although we support the use of RC techniques to guide decisions about concussion, we have concerns about the statistical computation and interpretation of various RC indices.
RC techniques were first described by Jacobson and Traux,1 and were designed to aid decision making about the significance of cognitive changes in patients in whom an injury or intervention had taken place. These and subsequent authors4,5 proposed that the most efficient way of determining whether an individual’s score on a specific cognitive measure had changed was to express the magnitude of change—that is, a change score—as a function of the normal variation found for that measure. Normal variation in performance on the cognitive measure was estimated from a group of similar subjects in whom no injury or intervention had occurred. Mathematically, the individual’s change in performance is …