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Re: st: Command -contrast- after -anova


From   David Airey <david.airey@Vanderbilt.Edu>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Command -contrast- after -anova
Date   Tue, 9 Dec 2008 09:18:21 -0600

see -anovacontrast- from ATS UCLA by Phil Ender

-Dave

On Dec 9, 2008, at 8:06 AM, Herve STOLOWY wrote:

Dear Statalisters:

I have some difficulties in using the -constrast- command (downloadable from ssc) after -anova-.

Here is my -anova- command line with the output.

anova return info risk info*risk if round>7 & round<26 & offer==1 & win==1, detail

 Factor        Value          Value          Value          Value
------------------------------------------------------------------------
 info          1 0            2 1

 risk          1 0            2 1

Number of obs = 2309 R-squared = 0.0401 Root MSE = .026537 Adj R-squared = 0.0389

Source | Partial SS df MS F Prob > F ----------- +---------------------------------------------------- Model | .067894615 3 .022631538 32.14 0.0000
                        |
info | .007341846 1 .007341846 10.43 0.0013 risk | .045207121 1 .045207121 64.20 0.0000 info*risk | .010246209 1 .010246209 14.55 0.0001
                        |
               Residual |  1.62318282  2305  .000704201
----------- +----------------------------------------------------
                  Total |  1.69107744  2308  .000732703


In the -contrast- command, I use the following syntax:

contrast return info risk, coeffs(1 1), if round>7 & round<26 & offer==1 & win==1

and it does not work.

I am almost sure that the figures after coeffs are wrong. To be honest, I do not understand very well the help file of -contrast-. (I tried the examples given in this file, based on auto.dta, but it returns an error message).

Does someone have some practice with -contrast-?

(I read the Stata manual and the differents threads in the Statalist. It seems that the -contrast- command should avoid using the command -test- with matrices after anova).

Best regards

Herve








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