What is a clinically meaningful difference?
Although much work is being done in this area, there is a lack of consensus on how clinical significance should be quantified. The FACIT approach has been to combine both anchor-based and distribution-based methods to derive estimates for our instruments. Distribution-based definitions are based on statistical distributions, e.g., effect size measures (Cohen, 1988) and other measures using means and standard deviations obtained from research studies or reference populations. Anchor-based interpretations of clinical meaningfulness are defined as measures that compare, or anchor, health-related quality of life changes (or differences) to other clinical changes (or groups). The most commonly used anchor-based measure is the global assessment originally described by researchers at McMaster University (Jaeschke, Singer & Guyatt, 1989). Another anchor that we have used is the ECOG performance status rating. A more extensive discussion of clinical significance and the FACIT Measurement System
