Ratio of means for analyzing continuous outcomes in meta-analysis performed as well as mean difference methods.

OBJECTIVE Meta-analyses of continuous outcomes typically use mean differences (MDs) or standardized mean differences (SMDs) (MD in pooled standard deviation units). Ratio of means (RoM) is an alternative effect measure that performs comparably in simulation. We compared treatment effects and heterogeneity for RoM, MD, and SMD using empiric data. STUDY DESIGN AND SETTING From the Cochrane Database (2008, issue 1), we included systematic reviews reporting continuous outcomes, selected the meta-analysis with the most (and ≥five) trials, and calculated MD (where possible), SMD, and RoM. For each pair of effect measures, we compared P-values separately for treatment effect and heterogeneity and assessed asymmetry of discordant pairs (statistically significant result for only one of two measures). RESULTS Two hundred thirty-two of 5,053 reviews were included. Measures demonstrated similar treatment effects, with ≤6% discordant pairs and no asymmetry. A 0.5 SMD increase corresponded to 22 (95% confidence interval: 19, 24)% increase using RoM. There was less heterogeneity in RoM vs. MD (n=143, P=0.007), SMD vs. RoM (n=232, P=0.005), and SMD vs. MD (n=143, P=0.004). Comparing discordant pairs, fewer meta-analyses showed significant heterogeneity with SMD vs. RoM (P=0.04), consistent with the known bias of SMD. CONCLUSION Empiric data from diverse meta-analyses demonstrate similar treatment effects and no large differences in heterogeneity of RoM compared with difference-based methods.

[1]  M. Hochberg,et al.  Acetaminophen for osteoarthritis. , 2003, The Cochrane database of systematic reviews.

[2]  Joseph Beyene,et al.  The ratio of means method as an alternative to mean differences for analyzing continuous outcome variables in meta-analysis: A simulation study , 2008 .

[3]  Jan O. Friedrich,et al.  Effect of mechanical ventilation in the prone position on clinical outcomes in patients with acute hypoxemic respiratory failure: a systematic review and meta-analysis , 2008, Canadian Medical Association Journal.

[4]  P. Onghena,et al.  Estimating the mean effect size in meta-analysis: Bias, precision, and mean squared error of different weighting methods , 2003, Behavior research methods, instruments, & computers : a journal of the Psychonomic Society, Inc.

[5]  I Olkin,et al.  Heterogeneity and statistical significance in meta-analysis: an empirical study of 125 meta-analyses. , 2000, Statistics in medicine.

[6]  R. Kunz,et al.  Meta-analysis: Effect of Monotherapy and Combination Therapy with Inhibitors of the ReninAngiotensin System on Proteinuria in Renal Disease , 2008, Annals of Internal Medicine.

[7]  W. G. Cochran The combination of estimates from different experiments. , 1954 .

[8]  Joseph Beyene,et al.  Meta-Analysis: Low-Dose Dopamine Increases Urine Output but Does Not Prevent Renal Dysfunction or Death , 2005, Annals of Internal Medicine.

[9]  Douglas G. Altman,et al.  Systematic Reviews in Health Care: Meta-Analysis in Context: Second Edition , 2008 .

[10]  M. Pittler Systematic Reviews in Health Care: Meta‐analysis in Context , 2010 .

[11]  L. Hedges,et al.  Statistical Methods for Meta-Analysis , 1987 .

[12]  Jacob Cohen Statistical Power Analysis for the Behavioral Sciences , 1969, The SAGE Encyclopedia of Research Design.

[13]  S. Thompson,et al.  Quantifying heterogeneity in a meta‐analysis , 2002, Statistics in medicine.

[14]  Lisa M. Schwartz,et al.  Misunderstandings about the effects of race and sex on physicians' referrals for cardiac catheterization. , 1999, The New England journal of medicine.

[15]  M. Meade,et al.  High frequency oscillation in patients with acute lung injury and acute respiratory distress syndrome (ARDS): systematic review and meta-analysis , 2010, BMJ : British Medical Journal.

[16]  Douglas G. Altman,et al.  Statistical Methods for Examining Heterogeneity and Combining Results from Several Studies in Meta‐Analysis , 2008 .

[17]  John T Granton,et al.  Effect of nitric oxide on oxygenation and mortality in acute lung injury: systematic review and meta-analysis , 2007, BMJ : British Medical Journal.

[18]  N. Laird,et al.  Meta-analysis in clinical trials. , 1986, Controlled clinical trials.

[19]  Jonathan J Deeks,et al.  Issues in the selection of a summary statistic for meta‐analysis of clinical trials with binary outcomes , 2002, Statistics in medicine.

[20]  D. Altman,et al.  Measuring inconsistency in meta-analyses , 2003, BMJ : British Medical Journal.

[21]  D. Wijeysundera,et al.  Use of gabapentin for perioperative pain control , 2007 .

[22]  G. Guyatt,et al.  The Impact of Prophylactic Dexamethasone on Nausea and Vomiting After Laparoscopic Cholecystectomy: A Systematic Review and Meta-Analysis , 2008, Annals of surgery.