Measuring inconsistency in meta-analyses
TLDR
A new quantity is developed, I 2, which the authors believe gives a better measure of the consistency between trials in a meta-analysis, which is susceptible to the number of trials included in the meta- analysis.Abstract:
Cochrane Reviews have recently started including the quantity I 2 to help readers assess the consistency of the results of studies in meta-analyses. What does this new quantity mean, and why is assessment of heterogeneity so important to clinical practice?
Systematic reviews and meta-analyses can provide convincing and reliable evidence relevant to many aspects of medicine and health care.1 Their value is especially clear when the results of the studies they include show clinically important effects of similar magnitude. However, the conclusions are less clear when the included studies have differing results. In an attempt to establish whether studies are consistent, reports of meta-analyses commonly present a statistical test of heterogeneity. The test seeks to determine whether there are genuine differences underlying the results of the studies (heterogeneity), or whether the variation in findings is compatible with chance alone (homogeneity). However, the test is susceptible to the number of trials included in the meta-analysis. We have developed a new quantity, I 2, which we believe gives a better measure of the consistency between trials in a meta-analysis.
Assessment of the consistency of effects across studies is an essential part of meta-analysis. Unless we know how consistent the results of studies are, we cannot determine the generalisability of the findings of the meta-analysis. Indeed, several hierarchical systems for grading evidence state that the results of studies must be consistent or homogeneous to obtain the highest grading.2–4
Tests for heterogeneity are commonly used to decide on methods for combining studies and for concluding consistency or inconsistency of findings.5 6 But what does the test achieve in practice, and how should the resulting P values be interpreted?
A test for heterogeneity examines the null hypothesis that all studies are evaluating the same effect. The usual test statistic …read more
Citations
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Meta-analysis of genome-wide association data and large-scale replication identifies additional susceptibility loci for type 2 diabetes
Eleftheria Zeggini,Laura J. Scott,Richa Saxena,Benjamin F. Voight,Jonathan Marchini,T Hu,de Bakker Piw.,de Bakker Piw.,de Bakker Piw.,Gonçalo R. Abecasis,Peter Almgren,Gregers S. Andersen,Kristin Ardlie,Kristina Bengtsson Boström,Richard N. Bergman,Lori L. Bonnycastle,Knut Borch-Johnsen,Knut Borch-Johnsen,Noël P. Burtt,H Chen,Peter S. Chines,Mark J. Daly,P Deodhar,Ding C-J.,Doney Asf.,William L. Duren,Katherine S. Elliott,Mike Erdos,Timothy M. Frayling,Rachel M. Freathy,Lauren Gianniny,Harald Grallert,Niels Grarup,Christopher J. Groves,Candace Guiducci,Torben Hansen,Christian Herder,Graham A. Hitman,Thomas Edward Hughes,Bo Isomaa,Anne U. Jackson,Torben Jørgensen,Augustine Kong,Kari Kubalanza,Finny G Kuruvilla,Finny G Kuruvilla,Johanna Kuusisto,Claudia Langenberg,Hana Lango,Torsten Lauritzen,Yun Li,Cecilia M. Lindgren,Cecilia M. Lindgren,Valeriya Lyssenko,Amanda F. Marvelle,Christine Meisinger,Kristian Midthjell,Karen L. Mohlke,Mario A. Morken,Andrew D. Morris,Narisu Narisu,Peter M. Nilsson,Katharine R. Owen,Palmer Cna.,Felicity Payne,Perry Jrb.,E Pettersen,Carl Platou,Inga Prokopenko,Inga Prokopenko,Lu Qi,Lu Qi,L Qin,Nigel W. Rayner,Nigel W. Rayner,Matthew G. Rees,J J Roix,A Sandbaek,Beverley M. Shields,Marketa Sjögren,Valgerdur Steinthorsdottir,Heather M. Stringham,Amy J. Swift,Gudmar Thorleifsson,Unnur Thorsteinsdottir,Nicholas J. Timpson,Nicholas J. Timpson,Tiinamaija Tuomi,Jaakko Tuomilehto,Mark Walker,Richard M. Watanabe,Michael N. Weedon,Cristen J. Willer,Thomas Illig,Kristian Hveem,Frank B. Hu,Frank B. Hu,Markku Laakso,Kari Stefansson,Oluf Pedersen,Oluf Pedersen,Nicholas J. Wareham,Inês Barroso,Andrew T. Hattersley,Francis S. Collins,Leif Groop,Leif Groop,Mark I. McCarthy,Mark I. McCarthy,Michael Boehnke,David Altshuler +110 more
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