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Re: st: problem with predicted probabilities


From   Nick Cox <njcoxstata@gmail.com>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   Re: st: problem with predicted probabilities
Date   Sun, 2 Feb 2014 10:19:50 +0000

As you want to use predicted probabilities in further work, use
-predict- to obtain them. -estat- here is just providing one report,
not the probabilities for future work. Start with -help logistic
postestimation-.

Nick
njcoxstata@gmail.com


On 2 February 2014 09:58, Witness Chirinda <witchirinda@gmail.com> wrote:

> I want to obtain some predicted probabilities after logistic
> regression, as attached. I want to use the predicted probabilities in
> my next step instead of observed prevalence since the latter are
> adjusted for other (socio-demographic) factors.
> My problem is that the when I run - estat classification- it giving 0s
> for + classification. I am sure I am doing it the wrong way somewhere.
> Please see below output. All variables used in the model have been
> recorded to be binary 1/0
>
> Thanks for any help!
> ------------------
>
>
> . logistic Health_stat  age maried wealth educat  place sex
>
> Logistic regression                               Number of obs   =       2339
>                                                            LR chi2(6)
>     =      50.61
>                                                            Prob > chi2
>     =     0.0000
> Log likelihood = -996.02516                       Pseudo R2       =     0.0248
> ------------------------------------------------------------------------------
>     Health_stat | Odds Ratio   Std. Err.      z    P>|z|     [95%
> Conf. Interval]
> -------------+----------------------------------------------------------------
>     age  | 1.109083   .0342696     3.35   0.001     1.043909    1.178326
> maried |  1.2134   .1962535     1.20   0.232     .8837556    1.666004
> Wealth |  1.430957   .1784661     2.87   0.004     1.120641    1.827203
> educat |  1.670411   .2010455     4.26   0.000     1.319397     2.11481
> place   |  .9334522   .1223134    -0.53   0.599     .7220318    1.206779
> sex     |   1.129008   .1324642     1.03   0.301     .8970722    1.420911
>
> . estat class
>
> Logistic model for poorSRHS
>               -------- True --------
> Classified |         D            ~D  |      Total
> -----------+--------------------------+-----------
>      +     |         0                 0  |          0
>       -     |       370          1969  |       2339
> -----------+--------------------------+-----------
>    Total   |       370          1969  |       2339
>
> Classified + if predicted Pr(D) >= .5
> True D defined as poorSRHS != 0
> --------------------------------------------------
> Sensitivity                     Pr( +| D)    0.00%
> Specificity                     Pr( -|~D)  100.00%
> Positive predictive value       Pr( D| +)       .%
> Negative predictive value       Pr(~D| -)   84.18%
> --------------------------------------------------
> 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| -)   15.82%
> --------------------------------------------------
> Correctly classified                        84.18%
> --------------------------------------------------
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