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When (Not) to Rely on the Reliable Change Index

The reliable change index (RCI) is a widely used statistical tool designed to account for measurement error when evaluating difference scores. Because of its conceptual simplicity and computational ease, it persists in research and applied psychology. However, researchers have repeatedly demonstrated ways that the RCI is insufficient or invalid for various applications. This is a problem in research and clinical psychology since this common tool is potentially problematic. The aims of this manuscript are to non-technically describe the formulation and assumptions of the RCI, to offer guidance as to when the RCI is (and is not) appropriate, and to identify what is needed for proper calculation of the RCI when it is used. Several criteria are identified to help determine whether the RCI is appropriate for a specific use. It is apparent that the RCI is the best available method only in a small number of situations, is frequently miscalculated, and produces incorrect inferences more often than simple alternatives, largely because it is highly insensitive to real changes. Specific alternatives are offered which may better operationalize common inferential tasks, including when more than two observations are available and when false negatives are equally costly to false positives.