title: Bias and small-study effects influence treatment effect estimates: a meta-epidemiological study in oral medicine.
abstract: OBJECTIVE
  To examine the influence of the following study characteristics on their study effect estimates: (1) indexing in MEDLINE, (2) language, and (3) design. For randomized trials, (4) trial size and (5) unequal randomization were also assessed.
  
  
  METHODS
  The CAtegorical Dental and Maxillofacial Outcome Syntheses meta-epidemiologic study was conducted. Eight databases/registers were searched up to September 2012 for meta-analyses of binary outcomes with at least five studies in the field of dental and maxillofacial medicine. The previously mentioned five study characteristics were investigated. The ratio of odds ratios (ROR) according to each characteristic was calculated with random-effects meta-regression and then pooled across meta-analyses.
  
  
  RESULTS
  A total of 281 meta-analyses were identified and used to assess the influence of the following factors: non-MEDLINE indexing vs. MEDLINE indexing (n = 78; ROR, 1.12; 95% confidence interval [CI]: 1.05, 1.19; P = 0.001), language (n = 61; P = 0.546), design (n = 24; P = 0.576), small trials (<200 patients) vs. large trials (≥200 patients) (n = 80; ROR, 0.92; 95% CI: 0.87, 0.98; P = 0.009) and unequal randomization (n = 36; P = 0.828).
  
  
  CONCLUSIONS
  Studies indexed in MEDLINE might present greater effects than non-indexed ones. Small randomized trials might present greater effects than large ones.
authors.affiliation: Department of Orthodontics, School of Dentistry, University of Bonn, Welschnonnenstr. 17, 53111, Bonn, Germany; Department of Oral Technology, School of Dentistry, University of Bonn, Welschnonnenstr. 17, 53111, Bonn, Germany; Clinical Research Unit 208, University of Bonn, 53111, Bonn, Germany. Electronic address: snpapage@gmail.com.
authors.forename: Spyridon N
authors.initials: SN
authors.lastname: Papageorgiou
authors.affiliation: Department of Periodontology and Geriatric Dentistry, Institute of Dentistry, University of Oulu, Medical Campus, Aapistie 3A, PO 5281, 90014, Oulu, Finland.
authors.forename: Georgios N
authors.initials: GN
authors.lastname: Antonoglou
authors.affiliation: Medical Research Methodology, Medical School, Aristotle University, PO 17034, 54210, Thessaloniki, Greece.
authors.forename: Elli
authors.initials: E
authors.lastname: Tsiranidou
authors.affiliation: Clinical Research Unit 208, University of Bonn, 53111, Bonn, Germany; Department of Periodontology, Operative and Preventive Dentistry, School of Dentistry, University of Bonn, Welschnonnenstr. 17, 53111, Bonn, Germany.
authors.forename: Søren
authors.initials: S
authors.lastname: Jepsen
authors.affiliation: Department of Orthodontics, School of Dentistry, University of Bonn, Welschnonnenstr. 17, 53111, Bonn, Germany; Clinical Research Unit 208, University of Bonn, 53111, Bonn, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Jäger
mesh_terms: D000043:Abstracting and Indexing; D015982:Bias; D016001:Confidence Intervals; D016021:Epidemiologic Studies; D006801:Humans; D016239:MEDLINE; D046650:Medical Subject Headings; D016017:Odds Ratio; D019242:Oral Medicine / Q000379:methods*; D017063:Outcome Assessment, Health Care; D016032:Randomized Controlled Trials as Topic
keywords: Dentistry; Effect size; Meta-analysis; Meta-epidemiologic study; Systematic review; systematic error