Sens/spec, +/-LRs, PPV/NPVs

Tom Yuen tom_yuen1 at YAHOO.COM
Tue Sep 11 22:52:51 UTC 2018

Many thanks to everyone's reply, especially from Dr Brush and John Ely for his thoughtful response.
I think the bottom line that my residents needed to answer was basically if there was any difference and/or advantage between sensitivity/specificity and +LR/-LR.  PPV/NPV, as John (Ely) pointed out is dependent on disease prevalence. 
But it seems to me, based on everyone's reply is that there doesn't seem to be much PRACTICAL difference between sens/spec and LR.  Just different ways of expressing essentially the same thing. (if I have this horribly wrong please correct me as I am giving a followup lecture Thursday and will be addressing the questions they have last week!)
Essentially a test with a high +LR and a high specificity- if positive in a patient with a moderate pretest prob of a disease, dramatically increases your posttest prob of them truly having the disease.  I think my residents were struggling (as was I) with whether it mattered which statistic (LR vs. spec/sens) we looked at- and it doesn't seem to matter.
Thank you again everyone, while I am a first-time poster I have been following this listserv for years and am humbled by the collective wisdom assembled here.
Tom Yuen, MD

Moderator: David Meyers, Board Member, Society to Improve Diagnosis in Medicine

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