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Re: st: Comparing results from two separate t-tests


From   David Airey <david.airey@Vanderbilt.Edu>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Comparing results from two separate t-tests
Date   Wed, 12 Mar 2008 14:49:43 -0500

.

I enjoyed Ithaca, when I was there!

Maybe you could use a regress instead of ttest. It will give the same answer as ttest, if you form a dummy variable for group membership and use it to predict your response variable. Estimates store will work with regress. You could also move on with regress to look at both political membership and treatment in the same model, without having to use multiple ttests.

-Dave

On Mar 12, 2008, at 2:30 PM, Geoff Wallace wrote:


Dear All,

I have had problems trying to test for whether the treatment effects for two groups of respondents (conservatives and liberals) in a social science experimental questionnaire I am using are significantly different. I used the -ttest- command to obtain the difference of means across the treatment and control group first for the conservative respondent subsample and then repeated the procedure for the liberal respondent subsample. I should also note that I used the –unpaired- option for each command since the data are not paired. The output from the two -ttest- commands yields a separate treatment effect for each subsample. However, I am having trouble figuring out how to use Stata to perform a corresponding ttest on the two separate difference of means. I tried using -est store- after each -ttest- command, but as I expected this option does not appear to work with –ttest-.

Any help would be much appreciated.

Best, Geoff

--
Geoffrey P.R. Wallace
Ph.D. Candidate
Department of Government
Cornell University

214 White Hall
Ithaca, NY 14850
t.202.302.4209
f.607.255.4530

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