On Mon, Oct 13, 2008 at 11:21 PM, Frank E Harrell Jr <[EMAIL PROTECTED]> wrote: > [EMAIL PROTECTED] 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. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
