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Re: st: predict or adjust after logistic?


From   "george hoffman" <ghoffman@mcw.edu>
To   <statalist@hsphsun2.harvard.edu>
Subject   Re: st: predict or adjust after logistic?
Date   Fri, 4 Apr 2003 14:02:42 -0600

this reply specifically to joanne garrett:
I have modified your wonderful predxcat to allow graphing of error bars when
there are two xv variables, and for including sd's not ci's (useful for
generating bland-altman-style intervals). i'd be happy to send it to you or
upload it somewhere. it's a little rough, but is a little less restrictive
than your version.
as for ver 8 graphics - they are so slow, i've been using gr7 and
powerpoint.

george hoffman
----- Original Message ----- 
From: Joanne Garrett
To: statalist@hsphsun2.harvard.edu
Sent: Thursday, April 03, 2003 9:00 AM
Subject: Re: st: predict or adjust after logistic?


predxcat and predxcon use the strandard error of the prediction. I plan
to update these programs to take advantage of the Stata 8.0 graphics as
soon as possible (in otherwords, when I figure out how to do it), and
will post them for anyone who is interested.
  Joanne Garrett

"Daniel, Gregory" wrote:
>
> I have just tried using the predxcat command, but I noticed that the
> confidence intervals seem too narrow and are pretty much the same as the
> CI's obtained when using:
>
> Adjust x2 x3 x4, by(x1) pr ci
>
> These CI's are calculated using the standard error from the predicted
index,
> not the predicted probability---correct?
>
>
> Christer wrote:
>
> Check out
> Predxcon or predxcat
> or
> logpred , regpred
> or
>
> The commands at Scott Long's Homepage (http://www.indiana.edu/~jslsoc/)
>
> Greg wrote:
>
> To predict  probabilities and 95% CIs of the predicted probabilities after
a
> multivariate  logistic model, I have previously used the following predict
> command:
>
> logistic y x1 x2  x3
> predict lr_index,  index
> predict se_index,  stdp
>
> gen p_hat =  exp(lr_index)/(1 +exp(lr_index))
> gen lb = lr_index -  invnorm(0.975)*se_index
> gen ub = lr_index +  invnorm(0.975)*se_index
> gen plb =  exp(lb)/(1+exp(lb))
> gen pub =  exp(ub)/(1+exp(ub))
> bysort x1: tabstat  p_hat plb pub
>
> However, this code  does not allow me to predict probabilities,
> by(x1), while keeping the other  covariates held constant, as the adjust
> command does.
>
> *
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