The RCI or Reliable Change Index is a measure of the change necessary to be considered statistically (and in most cases clinically) significant and not variation that is simply random. The assumption is that some variation is a naturally occurring and frequent phenomenon. When a score is “statistically” different than a comparator, that change is considered reliable and thus important to address in a clinical setting. To determine a reliable change, a distribution of differences is examined, the standard error of measurement along with the reliability of the measure is considered, and then a score difference at or above a defined level is judged significant. Any difference that is not significant can be considered a normal variation.
This and other helpful information is covered on ImPACT’s Raw Data and Composite Scores & Clinical Report Interpretation: Treatment Options.