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From |
Geoff Wallace <gw46@cornell.edu> |

To |
statalist@hsphsun2.harvard.edu |

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

Date |
Wed, 12 Mar 2008 16:26:06 -0400 |

I took the advice of both Maarten and David to try a regression route and this definitely provides a lot more flexibility and indeed gives the same substantive results.

I pretty much followed Maarten's suggestion of incorporating the interaction effect and that does the trick for testing the hypothesis of any difference between liberals and conservatives on the treatment without have to do multiple tests.

Thanks again to both of you!

Cheers, Geoff

Maarten buis wrote:

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

*

* For searches and help try:

* http://www.stata.com/support/faqs/res/findit.html

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* http://www.ats.ucla.edu/stat/stata/

-----------------------------------------

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/

-----------------------------------------

___________________________________________________________ Rise to the challenge for Sport Relief with Yahoo! For Good

http://uk.promotions.yahoo.com/forgood/

*

* For searches and help try:

* http://www.stata.com/support/faqs/res/findit.html

* http://www.stata.com/support/statalist/faq

* http://www.ats.ucla.edu/stat/stata/

-- 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 www.people.cornell.edu/pages/gw46/ <http://www.people.cornell.edu/pages/gw46/index.htm> * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**References**:**Re: st: Comparing results from two separate t-tests***From:*Maarten buis <maartenbuis@yahoo.co.uk>

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