“…6 The cut-off value was derived from a group of healthy volunteers. Studies from the United States have tended to use less than 35% as the cut-off value, which was used by Krishnamurthy et al 44,45 in the 1980s, while others have used values ranging from 40% to 65%. 32,34,41,46,47 The technique used to derive this value is of interest in this meta-analysis, as it may account for some of the significant heterogeneity observed among the studies.…”