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Re: st: is there a -regress- command equivalent to the pair matched ttest?


From   "Sam Norton" <samjnorton@googlemail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: is there a -regress- command equivalent to the pair matched ttest?
Date   Tue, 9 Dec 2008 15:12:14 +0000

Jose Maria

You can, if you really want to, use -xtmixed-.  Phil Enders
presentation at the West Coast Stata Users Group meeting in 2007 gives
an example of how to use -xtmixed- to estimate a RM-ANOVA.  Since
ANOVA is based on deviations from the grand mean -xi3- (available from
SSC) is needed to create effect coded variables.
http://www.stata.com/meeting/wcsug07/repeated_anova.pdf


--
Sam Norton
samjnorton@gmail.com
Research Student
Centre for Lifespan & Chronic Illness Research
University of Hertfordshire

2008/12/9 David Airey <david.airey@vanderbilt.edu>
>
> A paired ttest is equivalent to a repeated measures ANOVA with two levels to the repeated factor. You can see the regression equivalent below.
>
> webuse fuel, clear
> list, clean
> ttest mpg1 == mpg2
> local t = r(t)
> generate subject = _n
> list, clean
> reshape long mpg, i(subject) j(repeat)
> list, clean
> anova mpg repeat subject
> anova, regress
> test repeat
> local F = r(F)
> display `F' "=" `t'^2
> xi: regress mpg i.repeat i.subject
>
>
>
> On Dec 8, 2008, at 7:05 PM, josemaria wrote:
>
>> Dear Statalisters:
>> I am not sure whether it makes sense or not, but is there a sort of -regress- command that allows to conduct a pair-matched -ttest-, but with other independent variables?
>> I tried using -xtmixed-, but the result is not the same.
>> A contrived data set could be:
>> matching_identification  outcome ocasion variable_not_matched
>>                      1            1                1                0
>>                      1            2                2                0
>>                      2            3                1                0
>>                      2            5                2                1
>>                      3            2                1                0
>>                      3            4                2                1
>>                      4            6                1                1
>>                      4            5                2                1
>> To perform the pair-matched ttest  it is necessary to -reshape- and to use -ttest outcome1==outcome2-, losing the independent variable_not_matched.
>> Thank for any orientation.
>> Regards,
>> José Maria
>>
>> Jose Maria Pacheco de Souza, Professor Titular (aposentado)
>> Departamento de Epidemiologia/Faculdade de Saude Publica, USP
>> Av. Dr. Arnaldo, 715
>> 01246-904  -  S. Paulo/SP - Brasil
>> fones (11)3061-7747; (11)3768-8612
>> fax (11)3714-2403
>> www.fsp.usp.br/~jmpsouza
>> *
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>
>
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