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RE: st: predict or adjust after logistic?


From   "Daniel, Gregory" <GDaniel@healthcore.com>
To   "'statalist@hsphsun2.harvard.edu'" <statalist@hsphsun2.harvard.edu>
Subject   RE: st: predict or adjust after logistic?
Date   Thu, 3 Apr 2003 09:41:12 -0500

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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