title: Recent meta-analyses neglect previous systematic reviews and meta-analyses about the same topic: a systematic examination.
abstract: BACKGROUND
  As the number of systematic reviews is growing rapidly, we systematically investigate whether meta-analyses published in leading medical journals present an outline of available evidence by referring to previous meta-analyses and systematic reviews.
  
  
  METHODS
  We searched PubMed for recent meta-analyses of pharmacological treatments published in high impact factor journals. Previous systematic reviews and meta-analyses were identified with electronic searches of keywords and by searching reference sections. We analyzed the number of meta-analyses and systematic reviews that were cited, described and discussed in each recent meta-analysis. Moreover, we investigated publication characteristics that potentially influence the referencing practices.
  
  
  RESULTS
  We identified 52 recent meta-analyses and 242 previous meta-analyses on the same topics. Of these, 66% of identified previous meta-analyses were cited, 36% described, and only 20% discussed by recent meta-analyses. The probability of citing a previous meta-analysis was positively associated with its publication in a journal with a higher impact factor (odds ratio, 1.49; 95% confidence interval, 1.06 to 2.10) and more recent publication year (odds ratio, 1.19; 95% confidence interval 1.03 to 1.37). Additionally, the probability of a previous study being described by the recent meta-analysis was inversely associated with the concordance of results (odds ratio, 0.38; 95% confidence interval, 0.17 to 0.88), and the probability of being discussed was increased for previous studies that employed meta-analytic methods (odds ratio, 32.36; 95% confidence interval, 2.00 to 522.85).
  
  
  CONCLUSIONS
  Meta-analyses on pharmacological treatments do not consistently refer to and discuss findings of previous meta-analyses on the same topic. Such neglect can lead to research waste and be confusing for readers. Journals should make the discussion of related meta-analyses mandatory.
authors.affiliation: Department of Psychiatry and Psychotherapy, Technical University Munich, Klinikum rechts der Isar, Ismaningerstr 22, 81675, Munich, Germany. bartosz.helfer@gmail.com.
authors.forename: Bartosz
authors.initials: B
authors.lastname: Helfer
authors.affiliation: Complex Mental Illness Program, Centre for Addiction and Mental Health, Toronto, Canada. aaron.prosser@camh.ca.
authors.forename: Aaron
authors.initials: A
authors.lastname: Prosser
authors.affiliation: Department of Psychiatry and Psychotherapy, Technical University Munich, Klinikum rechts der Isar, Ismaningerstr 22, 81675, Munich, Germany. samaramyrto@gmail.com.
authors.forename: Myrto T
authors.initials: MT
authors.lastname: Samara
authors.affiliation: Department of Psychiatry, University of Oxford, Warneford Hospital, Oxford, UK. john.geddes@psych.ox.ac.uk.
authors.forename: John R
authors.initials: JR
authors.lastname: Geddes
authors.affiliation: Department of Psychiatry, University of Oxford, Warneford Hospital, Oxford, UK. andrea.cipriani@psych.ox.ac.uk.
authors.forename: Andrea
authors.initials: A
authors.lastname: Cipriani
authors.affiliation: Department of Psychiatry, University of Illinois at Chicago, Chicago, IL, USA. Jdavis@psych.uic.edu.
authors.forename: John M
authors.initials: JM
authors.lastname: Davis
authors.affiliation: Department of Hygiene and Epidemiology, University of Ioannina School of Medicine, Ioannina, Greece. dmavridi@cc.uoi.gr.|Department of Primary Education, University of Ioannina, Ioannina, Greece. dmavridi@cc.uoi.gr.
authors.forename: Dimitris
authors.initials: D
authors.lastname: Mavridis
authors.affiliation: Department of Hygiene and Epidemiology, University of Ioannina School of Medicine, Ioannina, Greece. georgia.salanti@gmail.com.
authors.forename: Georgia
authors.initials: G
authors.lastname: Salanti
authors.affiliation: Department of Psychiatry and Psychotherapy, Technical University Munich, Klinikum rechts der Isar, Ismaningerstr 22, 81675, Munich, Germany. Stefan.Leucht@lrz.tu-muenchen.de.
authors.forename: Stefan
authors.initials: S
authors.lastname: Leucht
mesh_terms: D006801:Humans; D015201:Meta-Analysis as Topic; D012196:Review Literature as Topic