CHA Family Medicine Residency

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UberDiagnosis – Chapter 5: the NNT and NNH

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You’ve heard about the “Number Needed to Treat” and the “Number Needed to Harm.” This statistic guesstimates how many people we need to screen in the clinic/hospital before we find a benefit or harm from a treatment.

Has your family or friends ever heard of the NNT? Have your patients ever asked: “what’s the NNH for this?


Well, this is an exciting year for biostatistics because NNT and NNH have hit pop culture and the mainstream media in a big way!


First, it started in October 2014 in the Wired Magazine. Then, PBS spread the word in December 2014.
Next, it hit the NY Times two months ago:How to Measure a Medical Treatment’s Potential for Harm


Then the AFP decided to get in on the action in this month’s AAFP: Introducing Medicine by the Numbers: A Collaboration of The NNT Group and AFP

This new series will appear in the online-only edition of AFP. Each month, medical editors from AFP and will select a topic to feature. We will use’s color-coding to quickly convey the relative merits of an intervention, and present the numbers for benefit and harm in a summary box. A discussion outlines the background evidence and the rationale for the rating, accompanied by key supporting references.



If you’ve worked with me, you might have heard me quoting things like “1 out of 8 to 9 people who are treated for AOM or sinusitis with antibiotics with GI upset and diarrhea.”

Where did I get these facts? How do I know them off the top of my head?

From the great website! In addition to facts on treatment, they also have launched a new section on diagnosis (and most relevantly here, on harms associated with overdiagnosis.)


Here are some of the relevant links to check out below. How often have you asked yourself a question about these clinical issues in the past month?

Primary Care: Diagnosis


Primary Care: Treatment



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