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# Re: st: An index for determining cut points using ROC

 From Steve Samuels To statalist@hsphsun2.harvard.edu Subject Re: st: An index for determining cut points using ROC Date Wed, 20 Jun 2012 21:38:03 -0400

```
You can compute both from first principles with Roger Newson's -senspec- (SSC)
or with any other command that outputs sensitivity and specificity. It's "Youden",
by the way, for WJ Youden.

http://www-history.mcs.st-and.ac.uk/Biographies/Youden.html

Here's a code excerpt that you can adapt.

*******************************************************
senspec mets bmxwaist, sensitivity(sens) specificity(spec)
gen youden= sens-(1-spec)
egen youdenmax= max(youden), by(gender)

gen dist = sqrt((1-sens)^2 + (1-spec)^2)
egen distmin = min(dist), by(gender)

/* Identify cut-offs */
list sens spec  youdenmax   dist   ///
bmxwaist if abs(youden -youdenmax)<0.0001
list sens spec  youden     distmin  ///
bmxwaist if abs(dist - distmin)<0.0001
********************************************************
Steve
sjsamuels@gmail.com

On Jun 20, 2012, at 9:13 PM, Alan Acock wrote:

I have a diagnostic test and want to predict which children will be school ready (0,1) based on the diagnostic test. ROC curves are great for this. There appear to be two indexes. Youdon's index and the point where the ROC curve is closest to 0,1.  Is there a way to compute either or both of these using Stata or a user written command? Findit youdon shows nothing.

Alan Acock

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