title: How large are the nonspecific effects of acupuncture? A meta-analysis of randomized controlled trials.
abstract: BACKGROUND
  While several recent large randomized trials found clinically relevant effects of acupuncture over no treatment or routine care, blinded trials comparing acupuncture to sham interventions often reported only minor or no differences. This raises the question whether (sham) acupuncture is associated with particularly potent nonspecific effects. We aimed to investigate the size of nonspecific effects associated with acupuncture interventions.
  
  
  METHODS
  MEDLINE, Embase, Cochrane Central Register of Controlled Clinical Trials and reference lists were searched up to April 2010 to identify randomized trials of acupuncture for any condition, including both sham and no acupuncture control groups. Data were extracted by one reviewer and verified by a second. Pooled standardized mean differences were calculated using a random effects model with the inverse variance method.
  
  
  RESULTS
  Thirty-seven trials with a total of 5754 patients met the inclusion criteria. The included studies varied strongly regarding patients, interventions, outcome measures, methodological quality and effect sizes reported. Among the 32 trials reporting a continuous outcome measure, the random effects standardized mean difference between sham acupuncture and no acupuncture groups was -0.45 (95% confidence interval, -0.57, -0.34; I2 = 54%; Egger's test for funnel plot asymmetry, P = 0.25). Trials with larger effects of sham over no acupuncture reported smaller effects of acupuncture over sham intervention than trials with smaller nonspecific effects (β = -0.39, P = 0.029).
  
  
  CONCLUSIONS
  Sham acupuncture interventions are often associated with moderately large nonspecific effects which could make it difficult to detect small additional specific effects. Compared to inert placebo interventions, effects associated with sham acupuncture might be larger, which would have considerable implications for the design and interpretation of clinical trials.
authors.affiliation: Institute of General Practice, Technische Universität München, Orleansstrasse 47, D-81667 Munich, Germany. klaus.linde@lrz.tum.de
authors.forename: Klaus
authors.initials: K
authors.lastname: Linde
authors.forename: Karin
authors.initials: K
authors.lastname: Niemann
authors.forename: Antonius
authors.initials: A
authors.lastname: Schneider
authors.forename: Karin
authors.initials: K
authors.lastname: Meissner
mesh_terms: D015670:Acupuncture Therapy / Q000379:methods*; D006801:Humans; D016032:Randomized Controlled Trials as Topic; D016896:Treatment Outcome