Assessing the amount of change in an outcome measure is not the same as assessing the importance of change

Purpose: To determine whether a difference exists between patients' self-ratings of amount of change and their self-ratings of importance of change. Methods: Eighty-eight patients receiving treatment of low-back pain completed two global rating of change (GRC) scales 4 to 6 weeks after their initial assessments. The scales were similar in format, differing only in that one asked respondents about the amount of change and the other about the importance of change. Results: Our analysis was restricted to 86 patients who reported improvement or no change. The chance-corrected agreement between patients' self-ratings of amount of change and their self-ratings of importance of change was low (κ=0.35; 95% CI, 0.23–0.48). Of 47 disagreements, 44 reported a greater importance of change than amount of change and 3 reported a greater amount of change than importance of change. Conclusions: Assessing the amount of change is not the same as assessing the importance of change. When the goal is to estimate important change, the reference standard should direct patients to judge the importance of the change.