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st: Re: RE: relative risk


From   "Wendell Joice" <wjoice@erols.com>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: Re: RE: relative risk
Date   Thu, 17 Jul 2003 10:25:33 -0400

Tom/Laurel,
Thanks for your helpful replies.
Tom,
And, yup...gulp...blush, I managed to confuse the incidence (Po) stat with
the p-value. Hopefully, I am awake now.
Thanks
----- Original Message ----- 
From: "Steichen, Thomas" <STEICHT@rjrt.com>
To: <statalist@hsphsun2.harvard.edu>
Sent: Wednesday, July 16, 2003 5:08 PM
Subject: st: RE: relative risk


> I don't see what you are referring to, Wendell.  The p-values
> (labeled "P>|Z|") appear to be changing to me.  What did not
> change is Po, which is defined as "the incidence of the outcome
> (dependent variable = 1) in the unexposed group."  This should not
> change based on # of predictors in the model.
>
> Tom

>I know nothing about this command, but it is probably just your large
sample
>size that is driving your overall results (Prob > chi2     = 0.0000 reports
>on the model). Your P>|z| for individual predictors varies.
>To check, take a  1% subsample of your dataset and run the same analysis.
With 180 or 190 obs, you might get a less sig model.
Laurel
Ann Arbor VAMC
>
> > -----Original Message-----
> > From: Wendell Joice [mailto:wjoice@erols.com]
> > Sent: Wednesday, July 16, 2003 4:55 PM
> > To: statalist@hsphsun2.harvard.edu
> > Subject: st: relative risk
> >
> >
> > 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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> > *   http://www.stata.com/support/statalist/faq
> > *   http://www.ats.ucla.edu/stat/stata/
> >
>
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