Use of the reliable change index to evaluate clinical significance in SF-36 outcomes.

The SF-36 Health Survey is the most widely used self-report measure of functional health. It is commonly used in both randomized controlled trials (RCT) and non-controlled evaluation of medical or other health services. However, determining a clinically significant change in SF-36 outcomes from pre-to-post-intervention, in contrast to statistically significant differences, is often not a focus of medical outcomes research. We propose use of the Reliable Change Index (RCI) in combination with SF-36 norms as one method for researchers, provider groups, and health care policy makers to determine clinically significant healthcare outcomes when the SF-36 is used as a primary measure. The RCI is a statistic that determines the magnitude of change score necessary of a given self-report measure to be considered statistically reliable. The RCI has been used to determine clinically significant change in mental health and behavioral medicine outcomes research, but is not widely applied to medical outcomes research. A usable table of RCIs for the SF-36 has been calculated and is presented. Instruction and a case illustration of how to use the RCI table is also provided. Finally, limitations and cautionary guidelines on using SF-36 norms and the RCI to determine clinically significant outcome are discussed.