Identical summary statistics were uncommon in randomized trials and cohort studies

Mark J Bolland* (Corresponding Author), Greg D Gamble, Alison Avenell, Andrew Grey

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

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OBJECTIVE: To examine the proposition that identical summary statistics (mean and/or SD) in different randomized controlled trials (RCT) or clinical cohorts can be explained by common or homogeneous source populations.

STUDY DESIGN: We estimated the probability of identical summary data in studies with high proportions of identical summary statistics, in simulations, and in control datasets.

RESULTS: The probability of both an identical mean and an identical SD for a variable in separate RCT is low (<~3%), unless the variable is rounded to 1 significant figure. In two RCT with identical summary statistics for 16 of 39 shared variables, simulations indicated the probability of the observed matches was <1 in 100,000. In 34 clinical cohorts with publication integrity concerns, the proportion of summary statistics from variables reported in ≥10 studies that were identical in ≥2 cohorts were high (42% for means, 52% for SD, and 29% for both), and improbable based on simulations and comparisons to control datasets.

CONCLUSIONS: The likelihood of multiple identical summary statistics within an individual RCT or across a body of RCT or cohort studies by the same research group is low, especially when both the mean, and the SD are identical, unless the variables are rounded to 1 significant figure.

Original languageEnglish
Pages (from-to)180-188
Number of pages9
JournalJournal of Clinical Epidemiology
Early online date15 May 2021
Publication statusPublished - 1 Aug 2021


  • Statistical method
  • research integrity
  • identical data
  • summary statistic
  • fabricated data
  • data integrity


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