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

Tom Yuen tom_yuen1 at YAHOO.COM
Sat Sep 8 17:12:59 UTC 2018


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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