title: Association between trial registration and treatment effect estimates: a meta-epidemiological study.
abstract: To increase transparency in research, the International Committee of Medical Journal Editors required, in 2005, prospective registration of clinical trials as a condition to publication. However, many trials remain unregistered or retrospectively registered. We aimed to assess the association between trial prospective registration and treatment effect estimates.
  
  
  
  This is a meta-epidemiological study based on all Cochrane reviews published between March 2011 and September 2014 with meta-analyses of a binary outcome including three or more randomised controlled trials published after 2006. We extracted trial general characteristics and results from the Cochrane reviews. For each trial, we searched for registration in the report's full text, contacted the corresponding author if not reported and searched ClinicalTrials.gov and the International Clinical Trials Registry Platform in case of no response. We classified each trial as prospectively registered (i.e. registered before the start date); retrospectively registered, distinguishing trials registered before and after the primary completion date; and not registered. Treatment effect estimates of prospectively registered and other trials were compared by the ratio of odds ratio (ROR) (ROR <1 indicates larger effects in trials not prospectively registered).
  
  
  
  We identified 67 meta-analyses (322 trials). Overall, 225/322 trials (70 %) were registered, 74 (33 %) prospectively and 142 (63 %) retrospectively; 88 were registered before the primary completion date and 54 after. Unregistered or retrospectively registered trials tended to show larger treatment effect estimates than prospectively registered trials (combined ROR = 0.81, 95 % CI 0.65-1.02, based on 32 contributing meta-analyses). Trials unregistered or registered after the primary completion date tended to show larger treatment effect estimates than those registered before this date (combined ROR = 0.84, 95 % CI 0.71-1.01, based on 43 contributing meta-analyses).
  
  
  
  Lack of trial prospective registration may be associated with larger treatment effect estimates.
authors.affiliation: Centre de Recherche Epidémiologie et Statistique, INSERM U1153, Hôpital Hôtel-Dieu, 1 place du Parvis Notre Dame, 75004, Paris, France. agnes.dechartres@aphp.fr.|Centre d'Epidémiologie Clinique, Hôpital Hôtel-Dieu, Assistance Publique-Hôpitaux de Paris, Paris, France. agnes.dechartres@aphp.fr.|Faculté de Médecine, Université Paris Descartes, Sorbonne Paris Cité, Paris, France. agnes.dechartres@aphp.fr.|French Cochrane Centre, Paris, France. agnes.dechartres@aphp.fr.
authors.forename: Agnès
authors.initials: A
authors.lastname: Dechartres
authors.affiliation: Centre de Recherche Epidémiologie et Statistique, INSERM U1153, Hôpital Hôtel-Dieu, 1 place du Parvis Notre Dame, 75004, Paris, France.|Centre d'Epidémiologie Clinique, Hôpital Hôtel-Dieu, Assistance Publique-Hôpitaux de Paris, Paris, France.|Faculté de Médecine, Université Paris Descartes, Sorbonne Paris Cité, Paris, France.|French Cochrane Centre, Paris, France.|Department of Epidemiology, Mailman School of Public Health, Columbia University, New York, USA.
authors.forename: Philippe
authors.initials: P
authors.lastname: Ravaud
authors.affiliation: Centre de Recherche Epidémiologie et Statistique, INSERM U1153, Hôpital Hôtel-Dieu, 1 place du Parvis Notre Dame, 75004, Paris, France.|French Cochrane Centre, Paris, France.
authors.forename: Ignacio
authors.initials: I
authors.lastname: Atal
authors.affiliation: Centre de Recherche Epidémiologie et Statistique, INSERM U1153, Hôpital Hôtel-Dieu, 1 place du Parvis Notre Dame, 75004, Paris, France.|Centre d'Epidémiologie Clinique, Hôpital Hôtel-Dieu, Assistance Publique-Hôpitaux de Paris, Paris, France.
authors.forename: Carolina
authors.initials: C
authors.lastname: Riveros
authors.affiliation: Centre de Recherche Epidémiologie et Statistique, INSERM U1153, Hôpital Hôtel-Dieu, 1 place du Parvis Notre Dame, 75004, Paris, France.|Centre d'Epidémiologie Clinique, Hôpital Hôtel-Dieu, Assistance Publique-Hôpitaux de Paris, Paris, France.|Faculté de Médecine, Université Paris Descartes, Sorbonne Paris Cité, Paris, France.|French Cochrane Centre, Paris, France.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Boutron
mesh_terms: D015982:Bias; D035843:Biomedical Research / Q000379:methods / Q000458:organization & administration; D002985:Clinical Protocols / Q000592:standards; D002986:Clinical Trials as Topic / Q000379:methods / Q000458:organization & administration; D006801:Humans; D015201:Meta-Analysis as Topic; D011642:Publications / Q000592:standards; D012107:Research Design / Q000592:standards*; D016896:Treatment Outcome
keywords: Bias; ClinicalTrials.gov; Meta-analysis; Meta-epidemiology; Randomised controlled trial; Registration