st: posthoc testing after ANOVA

[David Airey <david.airey@vanderbilt.edu>]

I've read the FAQ on post hoc testing after ANOVA,

http://www.stata.com/support/faqs/stat/test1.html

I think I'm beginning to appreciate testanova.

It would be nice if the FAQ related these Wald tests to those like 
Hsu's, Dunnett's, Scheffe's, Tukey's, etc. in various situations where 
one is preferred over the other. Obviously, a little exploration on my 
part would help.

I have a question related to the FAQ. Can one form _any_ linear 
combination of any of the cell means from any cell means model ANOVA?

For instance, if I have a split plot design,

                within-subject factor
                ---------------------
                stimulus1   stimulus2

drug     animal1  cell 1       2
         animal2    3          4

control  animal3    5          6
         animal4    7          8


This anova is: anova y drug/animal|drug stimulus drug*stimulus/, 
repeated(stimulus).

I was interested in the following comparison of cells after finding a 
drug*stimulus interaction significant:

((2-1)+(4-3)) / 2 = ((6-5)+(8-7)) / 2, average of differences between 
stim1 and stim2 by group

This test would be equivalent to transforming the data to difference 
scores (stimulus2-stimulus1), and then testing for a group difference 
between drug and control groups. It's easy to do the latter, but I 
wanted to know if test could do it directly and if the comparison I 
want is an allowable test.

Happy New Year,

-Dave

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