RE: st: Trouble with estat classification

["Dukes, Jonathan" <dukesj@wudosis.wustl.edu>]

I should preface with the fact that I used a dichotomized variable in the roctab (i.e. 0=Maternal Age LT 35, 1=Maternal Age GT 35).

roctab USabnormal matage, summary detail
------------------------------------------------------------------------------
                                           Correctly
Cutpoint      Sensitivity   Specificity   Classified          LR+          LR-
------------------------------------------------------------------------------
( >= 0 )          100.00%         0.00%       30.38%             1.0000
( >= 1 )           12.50%        80.00%       59.49%            0.6250       1.0938
( >  1 )            0.00%       100.00%       69.62%                                 1.0000
------------------------------------------------------------------------------

logistic USabnormal matage
estat classification

              -------- True --------
Classified |         D            ~D  |      Total
-----------+--------------------------+-----------
     +          |         0                  0  |          0
     -           |        24              55  |         79
-----------+--------------------------+-----------
   Total     |        24              55  |         79

Classified + if predicted Pr(D) >= .5
True D defined as USabnormal != 0
--------------------------------------------------
Sensitivity                     Pr( +| D)    0.00%
Specificity                     Pr( -|~D)  100.00%
Positive predictive value       Pr( D| +)       .%
Negative predictive value       Pr(~D| -)   69.62%
--------------------------------------------------
False + rate for true ~D        Pr( +|~D)    0.00%
False - rate for true D         Pr( -| D)  100.00%
False + rate for classified +   Pr(~D| +)       .%
False - rate for classified -   Pr( D| -)   30.38%
--------------------------------------------------
Correctly classified                        69.62%
--------------------------------------------------



Respectfully,


Jonathan



-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Richard Goldstein
Sent: Wednesday, February 05, 2014 1:27 PM
To: statalist@hsphsun2.harvard.edu
Subject: Re: st: Trouble with estat classification

there is nothing wrong here - they are just doing different things:
estat classification uses one cutpoint; -roctab- uses more than one as shown in the documentation

Rich

On 2/5/14, 2:17 PM, Dukes, Jonathan wrote:
> Dear Statalist,
>
> I used estat classification after a logistic regression to find the
> sensitivity,
specificity, and positive predictive value.  Using estat classification I get a sensitivity of 0% and a specificity of 100%. However, using roctab I get a sensitivity of 12.5% and specificity of 80%. Does anybody have an idea of what is wrong with the estat classification statement? Thank you for your help.
>
>
>
>
> Very Respectfully,
>
> Jonathan
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