Minimal Clinically Significant Difference

The minimal clinically significant difference is the smallest difference that clinicians and patients would care about. In choosing an HRQL instrument, it is important to know what is the smallest score difference on the instrument that represents the minimal clinically significant difference. It is possible for the minimal clinically significant difference to be larger than the difference that could be detected as statistically significant in a given situation (especially a clinical trial involving a large population), in which case a statistically, but not clinically, significant difference might be of little practical importance. For traditional clinical measures, such as the FEV1, clinicians and researchers typically have an understanding of what constitutes a minimal clinically important difference. Hence they would be likely to interpret an improvement of 50 mL in FEV1 as clinically important, even though it might not be statistically significant in a large sample study. A similar understanding of the minimal clinically significant difference is important when dealing with scores on HRQL and health status instruments. Determination of this value is specific to each instrument and can draw upon logical analysis of the properties of the instrument as well as upon data from a variety of experimental designs.