title: Majority of systematic reviews published in high-impact journals neglected to register the protocols: a meta-epidemiological study.
abstract: OBJECTIVE
  To describe the registration of systematic review (SR) protocols and examine whether or not registration reduced the outcome reporting bias in high-impact journals.
  
  
  METHODS
  We searched MEDLINE via PubMed to identify SRs of randomized controlled trials of interventions. We included SRs published between August 2009 and June 2015 in the 10 general and internal medicinal journals with the highest impact factors in 2013. We examined the proportion of SR protocol registration and investigated the relationship between registration and outcome reporting bias using multivariable logistic regression.
  
  
  RESULTS
  Among the 284 included reviews, 60 (21%) protocols were registered. The proportion of registration increased from 5.6% in 2009 to 27% in 2015 (P for trend <0.001). Protocol registration was not associated with outcome reporting bias (adjusted odds ratio [OR] 0.85, 95% confidence interval [CI] 0.39-1.86). The association between Preferred Reporting Items for Systematic review and Meta-Analysis (PRISMA) adherence and protocol registration was not statistically significant (OR 1.09, 95% CI 0.59-2.01).
  
  
  CONCLUSIONS
  Six years after the launch of the PRISMA statement, the proportion of protocol registration in high-impact journals has increased some but remains low. The present study found no evidence suggesting that protocol registration reduced outcome reporting bias.
authors.affiliation: Department of Healthcare Epidemiology, Graduate School of Medicine and Public Health, Kyoto University, Yoshida Konoe-cho, Sakyo-ku, Kyoto 606-8501, Japan.
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Tsujimoto
authors.affiliation: Hospital Care Research Unit, Hyogo Prefectural Amagasaki General Medical Center, Higashi-Naniwa-Cho 2-17-77, Amagasaki, Hyogo 660-8550, Japan.
authors.forename: Hiraku
authors.initials: H
authors.lastname: Tsujimoto
authors.affiliation: Department of Healthcare Epidemiology, Graduate School of Medicine and Public Health, Kyoto University, Yoshida Konoe-cho, Sakyo-ku, Kyoto 606-8501, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Kataoka
authors.affiliation: Department of Healthcare Epidemiology, Graduate School of Medicine and Public Health, Kyoto University, Yoshida Konoe-cho, Sakyo-ku, Kyoto 606-8501, Japan.
authors.forename: Miho
authors.initials: M
authors.lastname: Kimachi
authors.affiliation: Department of Healthcare Epidemiology, Graduate School of Medicine and Public Health, Kyoto University, Yoshida Konoe-cho, Sakyo-ku, Kyoto 606-8501, Japan.
authors.forename: Sayaka
authors.initials: S
authors.lastname: Shimizu
authors.affiliation: Department of Healthcare Epidemiology, Graduate School of Medicine and Public Health, Kyoto University, Yoshida Konoe-cho, Sakyo-ku, Kyoto 606-8501, Japan.
authors.forename: Tatsuyoshi
authors.initials: T
authors.lastname: Ikenoue
authors.affiliation: Department of Healthcare Epidemiology, Graduate School of Medicine and Public Health, Kyoto University, Yoshida Konoe-cho, Sakyo-ku, Kyoto 606-8501, Japan.
authors.forename: Shingo
authors.initials: S
authors.lastname: Fukuma
authors.affiliation: Department of Healthcare Epidemiology, Graduate School of Medicine and Public Health, Kyoto University, Yoshida Konoe-cho, Sakyo-ku, Kyoto 606-8501, Japan. Electronic address: yamamoto.yosuke.5n@kyoto-u.ac.jp.
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Yamamoto
authors.affiliation: Department of Healthcare Epidemiology, Graduate School of Medicine and Public Health, Kyoto University, Yoshida Konoe-cho, Sakyo-ku, Kyoto 606-8501, Japan.
authors.forename: Shunichi
authors.initials: S
authors.lastname: Fukuhara
mesh_terms: D015340:Epidemiologic Research Design; D006801:Humans; D055811:Journal Impact Factor; D016239:MEDLINE; D010506:Periodicals as Topic; D058028:Research Report; D000078202:Systematic Reviews as Topic
keywords: Meta-Analysis; Outcome reporting bias; PRISMA statement; Protocol registration; Systematic review; The PROSPERO registry