title: The journal impact factor as a predictor of trial quality and outcomes: cohort study of hepatobiliary randomized clinical trials.
abstract: OBJECTIVE
  To examine the association between the impact factor and characteristics of hepatobiliary randomized clinical trials.
  
  
  METHODS
  A cohort study of 530 hepatobiliary randomized clinical trials was performed. The journal impact factor was extracted from Science Citation Index. For each trial, we extracted the sample size, the quality of randomization and blinding methods, and the statistical significance of the primary outcome measure.
  
  
  RESULTS
  The median sample size was 45 participants (interquartile range 25-88). The allocation sequence generation was adequate in 273 trials (52%). Allocation concealment was adequate in 178 trials (34%). The primary outcome measure was statistically significant in 374 (71%) trials. Nonparametric analyses for trend indicated that the impact factor was significantly associated with the sample size (p < 0.01) and the proportion of trials with adequate allocation sequence generation (p < 0.01) or allocation concealment (p= 0.02). The impact factor was not significantly associated with the study outcome (p= 0.28).
  
  
  CONCLUSIONS
  The present study supports the use of the impact factor as a rough quality indicator. However, even trials in high impact journals may be small or may have inadequate quality. Critical appraisal of individual trials is always necessary, irrespective of the place of publication.
authors.affiliation: The Cochrane Hepato-Biliary Group, The Copenhagen Trial Unit, Centre for Clinical Intervention Research, Rigshospitalet, Copenhagen, Denmark.
authors.forename: Lise L
authors.initials: LL
authors.lastname: Gluud
authors.forename: Thorkild I A
authors.initials: TI
authors.lastname: Sørensen
authors.forename: Peter C
authors.initials: PC
authors.lastname: Gøtzsche
authors.forename: Christian
authors.initials: C
authors.lastname: Gluud
mesh_terms: D015706:Bibliometrics; D001660:Biliary Tract Diseases; D015331:Cohort Studies; D003627:Data Interpretation, Statistical; D006801:Humans; D008107:Liver Diseases; D018579:Patient Selection; D010506:Periodicals as Topic / Q000592:standards*; D011897:Random Allocation; D016032:Randomized Controlled Trials as Topic / Q000592:standards*; D012107:Research Design / Q000592:standards; D018401:Sample Size; D018709:Statistics, Nonparametric; D016896:Treatment Outcome