Lowering the statistical significance threshold of randomized controlled trials in three major general anesthesiology journals

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Purpose: The primary objective of our study was to determine how lowering a P-value threshold from 0.05 to 0.005 would affect the statistical significance of previously published randomized controlled trials (RCTs) in major anesthesiology journals. 

Methods: We searched the PubMed database for studies electronically published in 2020 within three major general anesthesiology journals as indexed by both Google Metrics and Scimago Journal & Country Rank. Studies included were RCTs published in 2020 in Anesthesiology, Anesthesia & Analgesia, and the British Journal of Anaesthesia; had a primary endpoint, and used a P value threshold to determine the effect of the intervention. We performed screening and data extraction in a masked duplicate fashion. 

Results: Ninety-one RCTs met inclusion criteria. The most frequently studied type of intervention was drugs (44/91, 48%). From the 91 trials, 99 primary endpoints, and thus P values, were obtained. Fifty-eight (59%) endpoints had a P value < 0.05 and 41 (41%) had a P value ≥ 0.05. Of the 58 primary endpoints previously considered statistically significant, 21 (36%) P values would maintain statistical significance at P < 0.005, and 37 (64%) would be reclassified as “suggestive.” 

Conclusions: Lowering a P value threshold of 0.05 to 0.005 would have altered one third of significance interpretations of RCTs in the surveyed anesthesiology literature. Thus, it is important for readers to consider post hoc probabilities when evaluating clinical trial results. Although the present study focused on the anesthesiology literature, we suggest that our results warrant further research within other fields of medicine to help avoid clinical misinterpretation of RCT findings and improve quality of care.

Original languageEnglish
Pages (from-to)1441-1448
Number of pages8
JournalCanadian Journal of Anesthesia
Issue number9
StatePublished - Sep 2023


  • P value
  • anesthesia
  • anesthesiology
  • randomized controlled trials
  • statistical significance


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