False-Positive Rates of Reliable Change Indices for Concussion Test Batteries: A Monte Carlo Simulation

Background: Neurocognitive testing is widely performed for the assessment of concussion. Athletic trainers can use preseason baselines with reliable change indices (RCIs) to ascertain whether concussed athletes' cognitive abilities are below preinjury levels. Although the percentage of healthy individuals who show decline on any individual test is determined by its RCI's confidence level (eg, 10% false-positive rate using an RCI with an 80% confidence interval), the expected rate of 1 or more significant RCIs across multiple indices is unclear. Objective: To use a Monte Carlo simulation procedure to estimate the normal rate (ie, base rate) of significant decline on 1 or more RCIs in multitest batteries. Results & Conclusion: For batteries producing 7 or more uncorrelated RCIs (80% confidence intervals), the majority of normal individuals would show significant declines on at least 1 RCI. Expected rates are lower for tests with fewer indices, higher inter-RCI correlations, and more stringent impairment criteria. These reference points can help testers interpret RCI output for multitest batteries.