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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