The recovery article states that “We changed our original protocol’s threshold score for being within a normal range on this measure from a score of ≥ 85 to a lower score as that threshold would mean that approximately half the general working age population would fall outside the normal range. The mean (S.D.) scores for a demographically representative English adult population were 86.3 (22.5) for males and 81.8 (25.7) for females. We derived a mean (S.D.) score of 84 (24) for the whole sample, giving a normal range of 60 or above for physical function” [5].
Having recovered differs from being within the normal range, and the PACE trial did not examine the “demographically representative English adult population.” Furthermore Bowling et al. [72] did not involve the “general working age population,” as the participants ages ranged from 16 to 85, with 28.6% aged 65 years or older. The PACE trial cohort’s mean age was 38 years [11] and therefore participants should be compared to healthy adults of the same age. According to the survey by Bowling et al. [72], which the PACE trial used, the mean physical functioning score for adults aged 35–44 years was 93.3, with a standard deviation of 13.4 [72] providing a normal score of ≥ 79.9, rather than ≥ 60, for physical functioning.
However, SF-36 physical functioning scores for healthy 38 year olds are not normally distributed but skewed to the right, with nearly everyone in the maximum range; and according to the BMJ’s statistical resources for readers, standard deviations will then be grossly inflated, are not a good measure of variability anymore and are therefore inappropriate for use [73], as highlighted by the fact that, Bowling et al.’s [72] survey of 2,000 patients, 1,200 and 400 had median scores of 100 and 90, respectively. The SF-36 physical functioning score decreases with age and ill health, almost 600 patients (28.6%) were aged 65 years or older, and 22% and 16% had chronic and acute health problems, respectively; therefore, the SF-36 physical functioning recovery score should have been 100 rather than 60 or more.