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Research Letter
November 6, 2018

Evaluation of Lowering the P Value Threshold for Statistical Significance From .05 to .005 in Previously Published Randomized Clinical Trials in Major Medical Journals

Author Affiliations
  • 1Oklahoma State University Center for Health Sciences, Tulsa
JAMA. 2018;320(17):1813-1815. doi:10.1001/jama.2018.12288

Lowering the threshold for statistical significance in medical research from a P value of .05 to .005 was recently proposed to reduce misinterpretation of study results.1,2P values less than .05 but greater than .005 would be reclassified as “suggestive.” What effect this proposal would have on the medical literature is unclear. We evaluated primary end points in randomized clinical trials (RCTs) published in 3 major general medical journals with high impact factors to determine how the new threshold could affect the interpretation of previously published RCTs.

We searched PubMed from January 1, 2017, to December 31, 2017, for phase 3 RCTs published in JAMA, Lancet, and New England Journal of Medicine (NEJM). We excluded single-group trials, pooled analyses, RCTs without P values, and RCTs that used Bayesian or noninferiority analyses. Two authors (C. W., J. S.) screened all trials.