title: Choice of effect measure for meta-analyses of dichotomous outcomes influenced the identified heterogeneity and direction of small-study effects.
abstract: OBJECTIVE
  The aim of this study was to compare the use of odds ratio (OR), risk ratio (RR), and risk difference (RD) in meta-analyses of dichotomous outcomes and assess their influence on their results.
  
  
  METHODS
  Initially, we included meta-analyses from a meta-epidemiologic database and reanalyzed them with OR, RR, and RD as summary metric. The primary outcomes were the effects of metric choice on the (1) statistical significance, (2) heterogeneity, and (3) Egger's test for publication bias. Additionally, meta-analyses that originally used OR were reanalyzed using RR to assess the differences in their results.
  
  
  RESULTS
  In the 235 meta-analyses (147 reviews) that were included, the conclusions in terms of significance rarely changed. On the other hand, use of OR displayed the lowest I(2) values (median 42%), followed by RR (+5.1%) and RD (+15.0%). The Egger's test was most often significant with RR (32%), followed by RD (29%) and OR (24%). Substitution of RR for OR led to a change of the observed effects in 3%, change of between-study heterogeneity in 6% to 24%, and change in Egger's test results in 7% of the cases, respectively.
  
  
  CONCLUSIONS
  The choice of metric for meta-analyses of dichotomous outcomes might influence the identified between-study heterogeneity and the results of Egger's test.
authors: Department of Orthodontics, School of Dentistry, University of Bonn, Welschnonnenstr. 17, Bonn 53111, Germany; Department of Oral Technology, School of Dentistry, University of Bonn, Welschnonnenstr. 17, Bonn 53111, Germany; Clinical Research Unit 208, University of Bonn, Welschnonnenstr. 17, Bonn 53111, Germany. Electronic address: snpapage@gmail.com.
authors: Spyridon N
authors: SN
authors: Papageorgiou
authors: Medical Research Methodology, Medical School, Aristotle University of Thessaloniki, University Campus, PO 17034, Thessaloniki 54210, Greece.
authors: Elli
authors: E
authors: Tsiranidou
authors: Department of Periodontology and Geriatric Dentistry, Institute of Dentistry, University of Oulu, Medical Campus, Aapistie 3A, PO 5281, Oulu 90014, Finland.
authors: Georgios N
authors: GN
authors: Antonoglou
authors: Clinical Research Unit 208, University of Bonn, Welschnonnenstr. 17, Bonn 53111, Germany; Experimental Dento-Maxillo-Facial Medicine, University of Bonn, Welschnonnenstr. 17, Bonn 53111, Germany.
authors: James
authors: J
authors: Deschner
authors: Department of Orthodontics, School of Dentistry, University of Bonn, Welschnonnenstr. 17, Bonn 53111, Germany; Clinical Research Unit 208, University of Bonn, Welschnonnenstr. 17, Bonn 53111, Germany.
authors: Andreas
authors: A
authors: Jäger
mesh_terms: D003627:Data Interpretation, Statistical; D006801:Humans; D015201:Meta-Analysis as Topic; D016017:Odds Ratio; D017594:Publication Bias; D012107:Research Design; D012196:Review Literature as Topic; D012306:Risk
keywords: Dentistry; Effect measure; Meta-analysis; Odds ratio; Risk difference; Risk ratio; Systematic reviews