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


From   Maarten buis <maartenbuis@yahoo.co.uk>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Comparing results from two separate t-tests
Date   Wed, 12 Mar 2008 19:58:20 +0000 (GMT)

Assuming that you have two dumies called treatment (1=treatment,
0=control) and liberal (1=liberal, 0=conservative), and that your
outcome variable is called y then you want:

anova y treatment liberal treatment*liberal

or:

xi: regress y i.treatment*i.liberal

The two are actually the same.

If you want to read more about this, than the term you are looking for
is "interaction effect".

Hope this helps,
Maarten



--- Geoff Wallace <gw46@cornell.edu> 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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> 


-----------------------------------------
Maarten L. Buis
Department of Social Research Methodology
Vrije Universiteit Amsterdam
Boelelaan 1081
1081 HV Amsterdam
The Netherlands

visiting address:
Buitenveldertselaan 3 (Metropolitan), room Z434

+31 20 5986715

http://home.fsw.vu.nl/m.buis/
-----------------------------------------


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