Reader beware: Interpreting post hoc analyses

Thursday, October 31, 2019

David L. Streiner, PhD, of McMaster University, Hamilton, Ont., and the University of Toronto, joins Blood & Cancer host David Henry, MD, of Pennsylvania Hospital, Philadelphia, to explain what a post hoc analysis is and why it should be interpreted with caution.

Plus, in Clinical Correlation, Ilana Yurkiewicz, MD, of Stanford (Calif.) University, explores what to tell patients when it comes to prognostic scoring system results.

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This week in Oncology:

In rectal cancer, fragmented care linked to lower survival
by Jim Kling, reporting from Clinical Congress 2019.

Post hoc analyses

What is a post hoc analysis? Analyzing data after a study has already had conclusions made and looking for patterns that were not prespecified.

Dr. Streiner’s advice for researchers: Pick a small number of primary outcomes and develop a narrow hypothesis. Then use post hoc analysis as a means of assessing future questions that can be investigated in a subsequent study.

Dr. Streiner’s advice for clinicians: Treat a post hoc analysis as a hypothesis that requires further study. It should be viewed with some degree of suspicion because it may have been significant only by chance.

Show notes by Ronak Mistry, DO, resident in the department of internal medicine, University of Pennsylvania, Philadelphia.


Marcus R et al. Obinutuzumab for the first-line treatment of follicular lymphoma. N Engl J Med. 2017;377:1331-44.

Crawford ED et al. Comorbidity and mortality results from a randomized prostate cancer screening trial. J Clin Oncol. 2011;29:355-61.

Streiner DL et al. Size, follow-up, data analysis – good; post hoc analysis, interpretation – not so good. Commun Oncol. 2011;8:379-80.

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Podcast Participants

David Henry, MD
David Henry, MD, FACP, is a clinical professor of medicine at the University of Pennsylvania and vice chairman of the department of medicine at Pennsylvania Hospital in Philadelphia. He received his bachelor’s degree from Princeton University and his MD from the University of Pennsylvania, then completed his internship, residency, and fellowship at the Hospital of the University of Pennsylvania. After 2 years as an attending in the U.S. Air Force, he was drawn to practicing as a hem-onc because of the close patient contact and interaction, and his belief that, win or lose with each patient, one can always make a difference in their care and lives. Follow Dr. Henry on Twitter: @davidhenrymd. Dr. Henry reported being on the advisory board for Amgen, AMAG Pharmaceuticals, and Pharmacosmos. He reported institutional funding from the National Institutes of Health and FibroGen.