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Re: st: difference between -test- and -contrast- in Statat 12


From   Richard Williams <richardwilliams.ndu@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: difference between -test- and -contrast- in Statat 12
Date   Thu, 25 Aug 2011 23:53:51 -0400

At 10:15 PM 8/25/2011, Ricardo Ovaldia wrote:

I am using the new -contrast- command in Stata 12 to test a contrast after ANOVA and I get different p-values than when using -test- although the marginal means are the same.

Confirming my earlier theory (I think): The value of both the F and the chi-square test stat is .72867669. I am one of 3 people in the world who still uses Stataquest, so using its handy calculator functions,

. tablesq F 1 63 .72867669

F(1,63) = .72867669
       Pr(F <= .72867669) = 0.6035
       Pr(F >= .72867669) = 0.3965

. tablesq X 1 .72867669

X(1) = .72867669
       Pr(X <= .72867669) = 0.6067
       Pr(X >= .72867669) = 0.3933

Those are the same p values you reported.

As a sidelight, I could probably let Stataquest rest in peace if Stata just had a nice calculator menu like Stataquest does. I know there are commands out there that do the same thing but it is too much trouble to hunt around for them.

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Richard Williams, Notre Dame Dept of Sociology
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