help teaching about likelihood ratios, sensitivity, positive pred values!

Tom Benzoni benzonit at GMAIL.COM
Sat Sep 8 21:11:58 UTC 2018

John Brush, The Art of the Science of Medicine
ISBN-13: 978-0990961376
Says it better than I can.
tom benzoni

On Sat, Sep 8, 2018 at 12:29 PM Tom Yuen <
0000001243181998-dmarc-request at> wrote:

> Hello,
> Young faculty here just tasked with teaching new family medicine residents
> diagnostic reasoning. During my inaugural lecture on LR (likelihood
> ratios)/PPV (positive predictive value)/NPV (negative predictive value) and
> sens/specificity, a newly minted 2nd year resident posed this comment:
>  "I understand that mathematically and statistically these are all subtly
> different. But in the real world, when I'm admitting someone for chest
> pain- all these things are pretty much the same.  A very sensitive test
> that is negative means that the likelihood of the disease is very low.
> Most sensitive tests also are low likelihood rations and very good NPV.
> It's all pretty much the same in the real world. Why learn how these are
> different?”
> As an example another resident quoted these numbers (I have yet to confirm
> them, but irregardless her point was):  A negative troponin has a
> sensitivity of 95% and a neg LR of 0.06 and a NPV of 98% for acute
> myocardial infarction.  What does it matter which statistic you use, they
> all "say the same thing”.
> Intellectually I was able to dig myself out, at least with NPV since it
> depends on the prevelence of the disease. But I did not have a more
> eloquent answer for LR and sensitivity.  And it all rang hollow to me as I
> tried to put myself in their shoes.
> Does anyone have any suggestions, or tips? Or reading? Or are they right
> that these numbers are tell pretty much the same tale when being used by a
> on-call resident at 2am in the "real world”?
> Thanks. Tom Yuen, MD
> Faculty Crozer Family Medicine Residency
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