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st: relative risk


From   "Wendell Joice" <wjoice@erols.com>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: relative risk
Date   Wed, 16 Jul 2003 16:55:15 -0400

I am using Stata 7 and the -relrisk- (ado) command in conjunction
ith  -logistic-. I note that, for my data, the p value (for a given
covariate) never changes, regardless of how many or which variables I add to
the model. For example, in the data below, I am using a dependent variable
(psyment) with a covariate (racewbh). The relative risk ratios for
_Iracewbh_2  &  _Iracewbh_3 change as I add other covariates to the model;
but the p value for these two variables never changes  (see small and large
models below).

Is this the way it should be or am I in error with my data? My usage of
the -relrisk- command?
Is there a simple way to check (verify) the output of the -relrisk- command?

Thanks,
Wendell Joice



SMALL MODEL

xi: logistic psyment i.racewbh if csample==1
      i.racewbh         _Iracewbh_1-3       (naturally coded; _Iracewbh_1
omitted)

      Logit estimates                                   Number of obs   =
19295
                                                        LR chi2(2)      =
68.54
                                                        Prob > chi2     =
0.0000
      Log likelihood = -12961.957                       Pseudo R2       =
0.0026

      ----------------------------------------------------------------------
--------
           psyment | Odds Ratio   Std. Err.      z    P>|z|     [95% Conf.
Interval]
      -------------+--------------------------------------------------------
--------
       _Iracewbh_2 |   .6429203   .0385832    -7.36   0.000     .5715766
.723169
       _Iracewbh_3 |   .7907062   .0466184    -3.98   0.000     .7044174
.8875651
      ----------------------------------------------------------------------
--------

    relrisk
                                      Po             Rel Risk       Lower
Limit    Upper Limit
      RR _Iracewbh_2:    0.066          0.658          0.588          0.737
      RR _Iracewbh_3:    0.065          0.802          0.718          0.894


LARGER MODEL BELOW

xi: logistic psyment i.racewbh i.physpecy i.psydin2 i.phytimec i.chrcadg
i.di
      > agsrvc  i.acutcadg i.newinsur i.likreccdg i.psydrnumx i.agecatc
i.GEOGREGN i.
      > yearmhp if csample==1

(output abbreviated)

      Logit estimates                                   Number of obs   =
18110
                                                        LR chi2(30)     =
11484.07
                                                        Prob > chi2     =
0.0000
      Log likelihood = -6465.4055                       Pseudo R2       =
0.4704

      ----------------------------------------------------------------------
--------
           psyment | Odds Ratio   Std. Err.      z    P>|z|     [95% Conf.
Interval]
      -------------+--------------------------------------------------------
--------
       _Iracewbh_2 |   .8734043   .0805943    -1.47   0.142     .7289031
1.046552
       _Iracewbh_3 |   .9309302   .0823622    -0.81   0.419     .7827242
1.107199
      _Iphyspecy_2 |   .5840736   .0408614    -7.69   0.000     .5092348
.6699109
      _Iphyspecy_3 |   10.01045   .8514816    27.08   0.000     8.473265
11.82649
      ..........................................Output
abbreviated......................

       _Iyearmhp_6 |   .4989542   .0376058    -9.22   0.000     .4304337
.5783824
      ----------------------------------------------------------------------
--------

    relrisk
                                      Po             Rel Risk       Lower
Limit    Upper Limit
      RR _Iracewbh_2:    0.066          0.881          0.742          1.043
      RR _Iracewbh_3:    0.065          0.935          0.794          1.100
      RR _Iphyspecy_2:   0.168          0.628          0.555          0.709
      RR _Iphyspecy_3:   0.016          8.764          7.579          10.100
      ............................................Output
abbreviated...............................
      RR _Iyearmhp_5:    0.059          0.773          0.667          0.896
      RR _Iyearmhp_6:    0.061          0.515          0.446          0.594



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