st: RE: restricting the number of groups within a t-test [was: something unreadable]

[Maarten buis <maartenbuis@yahoo.co.uk>]

--- Amal Khanolkar wrote:
> I have a categorical variable with 4 sub categories. I was wondering if 
> its possible to compare means of just 2 categories using the t-test?
> When I looked up help for t-test, there didn't seem to be any options
> to tell stata to restrict the test to means of just 2 categories.

I guess that the easiest way is to create a new variable that has the
observed values when an observation belongs to one of the two groups 
you want to compare and a missing value otherwise. So in the example
below I wanted to compare autos with repair status 2 and 3. This is
what the -if inlist(rep78, 2, 3)- part does. For more see 
-help inlist-.

*----------- begin example -------------
sysuse auto, clear
gen rep2 = rep78 if inlist(rep78, 2,3)
ttest mpg, by(rep2)
*------------ end example --------------
(For more on examples I sent to the Statalist see: 
http://www.maartenbuis.nl/example_faq )

Hope this helps,
Maarten

--------------------------
Maarten L. Buis
Institut fuer Soziologie
Universitaet Tuebingen
Wilhelmstrasse 36
72074 Tuebingen
Germany

http://www.maartenbuis.nl
--------------------------


      

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