Re: Patient reported outcome measures: how are we feeling today?
An example of regression to the mean?
John Appleby's figure, a plot of preoperative score against "Health gain" (postoperative score-preoperative score) shows a tendency for better preoperative health to be associated with smaller health gains. Isn't this an example of regression to the mean  and so wouldn't a more preferable way of depicting any association be via a plot of postoperative score against the mean of both the preoperative and postoperative scores?
Perhaps Bland or Altman could comment!
 Bland JM, Altman DG. (1994) Some examples of regression towards the mean. 309, 780.
 Bland JM, Altman DG. (1986).Comparing methods of measurement: why plotting difference against standard method is misleading. Lancet, 346, 1085-7.
Competing interests: No competing interests