A systematic review 1 included 191 studies. The average age of the patients was between 29 and 76 years. 69% of the studies included random assignment to treatment condition.
Significant beneficial effects of small to medium magnitude were found on recovery (0.43), pain (0.38) and psychological distress (0.36). For these same outcomes, based on the direction of the effect, the percentages of studies indicating beneficial effects ranged from 79 to 84%. Length of stay in hospital decreased by an average of 1.5 days in the treatment groups (based on 76 studies).
Comment: The quality of evidence is downgraded by study quality (no mention in the review on how data was extracted from the studies and how studies were combined)
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