[R] Fw: Logistic regresion - Interpreting (SENS) and (SPEC)

[Gabor Grothendieck]

On Mon, Oct 13, 2008 at 11:21 PM, Frank E Harrell Jr
<f.harrell at vanderbilt.edu> wrote:
> cryan at binghamton.edu wrote:
>>
>> I recall a concept of Snout:  sensitivity that is high enough to
>> essentially rule out the presence of disease.  And Spin:  specificity that
>> is high enough to essentially rule in the presence of disease.
>>
>> So perhaps the below is backwards?  The higher the sensitivity, the
>> greater the NPV?  And the higher the specificity, the
>
> greater the PPV?
>>
>
> Why should we care when we can directly estimate Prob(disease | test results
> and risk factors)?

Sensitivity and specificity are functions of the test only but ppv is
also a function
of the disease prevalence.   Just change the prevalence and the ppv changes
whereas sensitivity and specificity are invariant.

If our aim is to assess a test one wants a measure that only measures the test
itself.