title: Accounting for correlation in network meta-analysis with multi-arm trials.
abstract: Multi-arm trials (trials with more than two arms) are particularly valuable forms of evidence for network meta-analysis (NMA). Trial results are available either as arm-level summaries, where effect measures are reported for each arm, or as contrast-level summaries, where the differences in effect between arms compare with the control arm chosen for the trial. We show that likelihood-based inference in both contrast-level and arm-level formats is identical if there are only two-arm trials, but that if there are multi-arm trials, results from the contrast-level format will be incorrect unless correlations are accounted for in the likelihood. We review Bayesian and frequentist software for NMA with multi-arm trials that can account for this correlation and give an illustrative example of the difference in estimates that can be introduced if the correlations are not incorporated. We discuss methods of imputing correlations when they cannot be derived from the reported results and urge trialists to report the standard error for the control arm even if only contrast-level summaries are reported. Copyright © 2012 John Wiley & Sons, Ltd.
authors.affiliation: School of Social and Community Medicine, University of Bristol, Canynge Hall, 39 Whatley Road, Bristol, BS8 2PS, UK. angelo.franchini@bristol.ac.uk.
authors.forename: A J
authors.initials: AJ
authors.lastname: Franchini
authors.affiliation: School of Social and Community Medicine, University of Bristol, Canynge Hall, 39 Whatley Road, Bristol, BS8 2PS, UK.
authors.forename: S
authors.initials: S
authors.lastname: Dias
authors.affiliation: School of Social and Community Medicine, University of Bristol, Canynge Hall, 39 Whatley Road, Bristol, BS8 2PS, UK.
authors.forename: A E
authors.initials: AE
authors.lastname: Ades
authors.affiliation: Mapi Group, 180 Canal Street, Boston, MA, 02114, USA.|Department of Medicine, Tufts University School of Medicine, 136 Harrison Avenue, Boston, MA, 02111, USA.
authors.forename: J P
authors.initials: JP
authors.lastname: Jansen
authors.affiliation: School of Social and Community Medicine, University of Bristol, Canynge Hall, 39 Whatley Road, Bristol, BS8 2PS, UK.
authors.forename: N J
authors.initials: NJ
authors.lastname: Welton
keywords: meta‐analysis; mixed treatment comparison; multiple treatment comparison; network meta‐analysis