Interpretation of Changes in Health-related Quality of Life: The Remarkable Universality of Half a Standard Deviation

Background. A number of studies have computed the minimally important difference (MID) for health-related quality of life instruments. Objective. To determine whether there is consistency in the magnitude of MID estimates from different instruments. Methods. We conducted a systematic review of the literature to identify studies that computed an MID and contained sufficient information to compute an effect size (ES). Thirty-eight studies …