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st: problem with predicted probabilities


From   Witness Chirinda <witchirinda@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: problem with predicted probabilities
Date   Sun, 2 Feb 2014 11:58:46 +0200

Dear Statalist
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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