Influence of control group on effect size in trials of acupuncture for chronic pain: a secondary analysis of an individual patient data meta-analysis.
BACKGROUND
In a recent individual patient data meta-analysis, acupuncture was found to be superior to both sham and non-sham controls in patients with chronic pain. In this paper we identify variations in types of sham and non-sham controls used and analyze their impact on the effect size of acupuncture.


METHODS
Based on literature searches of acupuncture trials involving patients with headache and migraine, osteoarthritis, and back, neck and shoulder pain, 29 trials met inclusion criteria, 20 involving sham controls (n = 5,230) and 18 non-sham controls (n = 14,597). For sham controls, we analysed non-needle sham, penetrating sham needles and non-penetrating sham needles. For non-sham controls, we analysed non-specified routine care and protocol-guided care. Using meta-regression we explored impact of choice of control on effect of acupuncture.


RESULTS
Acupuncture was significantly superior to all categories of control group. For trials that used penetrating needles for sham control, acupuncture had smaller effect sizes than for trials with non-penetrating sham or sham control without needles. The difference in effect size was -0.45 (95% C.I. -0.78, -0.12; p = 0.007), or -0.19 (95% C.I. -0.39, 0.01; p = 0.058) after exclusion of outlying studies showing very large effects of acupuncture. In trials with non-sham controls, larger effect sizes associated with acupuncture vs. non-specified routine care than vs. protocol-guided care. Although the difference in effect size was large (0.26), it was not significant with a wide confidence interval (95% C.I. -0.05, 0.57, p = 0.1).


CONCLUSIONS
Acupuncture is significantly superior to control irrespective of the subtype of control. While the choice of control should be driven by the study question, our findings can help inform study design in acupuncture, particularly with respect to sample size. Penetrating needles appear to have important physiologic activity. We recommend that this type of sham be avoided.
Department of Health Sciences, University of York, York, United Kingdom.
Hugh
H
MacPherson
Memorial Sloan-Kettering Cancer Center, New York, New York, United States of America.
Emily
E
Vertosick
Faculty of Medicine, Primary Care and Population Sciences, University of Southampton, Southampton, United Kingdom.
George
G
Lewith
Institute of General Practice, Technische Universität München, Munich, Germany.
Klaus
K
Linde
Group Health Research Institute, Seattle, Washington, United States of America.
Karen J
KJ
Sherman
Center for Complementary and Integrative Medicine, University Hospital Zurich, Zurich, Switzerland; Institute for Social Medicine, Epidemiology and Health Economics, Charité - Universitätsmedizin, Berlin, Germany.
Claudia M
CM
Witt
Memorial Sloan-Kettering Cancer Center, New York, New York, United States of America.
Andrew J
AJ
Vickers
D015670:Acupuncture Therapy / Q000706:statistics & numerical data*; D059350:Chronic Pain / Q000628:therapy*; D035061:Control Groups; D015987:Effect Modifier, Epidemiologic; D006801:Humans; D009339:Needles / Q000706:statistics & numerical data; D012044:Regression Analysis