title: Biased and inadequate citation of prior research in reports of cardiovascular trials is a continuing source of waste in research.
abstract: OBJECTIVE
  We assessed citation of prior research over time and the association of citation with the agreement of results between the trial being reported and the prior trial.
  
  
  METHODS
  Groups of pharmacologic trials in cardiovascular disease were created using meta-analyses, and we assessed citation within these groups. We calculated the proportion of prior trials cited, the proportion of study participants captured in citations, and agreement of results between citing and cited trials.
  
  
  RESULTS
  Analysis included 86 meta-analyses with 580 trials published between 1982 and 2011. Reports of trials cited 25% (median; 95% confidence interval [CI], 23-27%) of prior trials, capturing 31% (95% CI, 25-36%) of trial participants. Neither measure differed by publication of the citing trial before vs. after 2005. Prior trials with results that agreed with the reports of trials (supportive trials) were significantly more likely to be cited than nonsupportive trials (relative risk 1.45; 95% CI, 1.30-1.61, P < 0.001).
  
  
  CONCLUSIONS
  Selective undercitation of prior research continues; three quarters of existing evidence is ignored. This source of waste may result in unnecessary, unethical, and unscientific studies.
authors.affiliation: Department of Epidemiology, Johns Hopkins University, 615 N. Wolfe Street, Baltimore, MD 21205, USA. Electronic address: veronica.ivey@gmail.com.
authors.forename: Veronica I
authors.initials: VI
authors.lastname: Sawin
authors.affiliation: Division of General Internal Medicine, Department of Medicine, Johns Hopkins University, 624 N. Broadway, Baltimore, MD, USA.
authors.forename: Karen A
authors.initials: KA
authors.lastname: Robinson
mesh_terms: D015982:Bias; D035843:Biomedical Research / Q000706:statistics & numerical data*; D002318:Cardiovascular Diseases; D003627:Data Interpretation, Statistical; D006801:Humans; D016032:Randomized Controlled Trials as Topic / Q000706:statistics & numerical data*
keywords: Cardiovascular disease; Citation bias; Evidence-based research; Meta-analysis; Randomized controlled trials; Reporting bias; Research design