# st: Repeated Measures Manova contrasts

 From A Noyb To statalist@hsphsun2.harvard.edu Subject st: Repeated Measures Manova contrasts Date Tue, 23 Oct 2007 09:51:13 -0700 (PDT)

```I ordinarily use SPSS, and am new to Stata; this is my
first  post to this list.  Could  anyone refer me to
resources for understanding the matrix command, more
particularly for _laying out the contrast coefficients
depending on the  number of levels of the IV and DV in
MANOVA_?

I hope my questions  are proper ones for this list and
are not too basic.  I am doing a Manova and am most
interested in the time by treatment interaction.  I am
baffled by the  contrasts described in the worked
example at
http://www.ats.ucla.edu/stat/stata/faq/manovarep.htm
.

Any help in understanding how to write contrasts in
such a situation would be much appreciated.  The
online
Stata manual doesn't provide much guidance nor have
other web resources/our university library.

Thank you,

Sandy

Below is a more detailed description of the questions
data, in case anyone is inclined/willing to give their
two cents.

WORKED EXAMPLE

input s a y1 y2 y3 y4
1 1 3 4 7  7
2 1 6 5 8  8
3 1 3 4 7  9
4 1 3 3 6  8
5 2 1 2 5 10
6 2 2 3 6 10
7 2 2 4 5  9
8 2 2 3 6 11
end

manova y1 y2 y3 y4 = a
mat ymat = (1,0,0,-1\0,1,0,-1\0,0,1,-1)
mat list ymat

I  don't understand how these coefficients measure the
interaction, it looks like they just compare each of
y1 to y3 in turn to y4.

MY DATA
My dataset has three repeat measurements of a number
of variables and several IVs of  differing levels.

DVTime1  DVTime2  DVTime3  IV1 IV2
3        4        3        1    1
1        2        4        1    2
2        1        5        1    3
3        4        6        1    1
3        5        4        2    2
2        4        3        2    4
3        1        5        2    2
1        4        4        2    2
3        4        4        2    1

The main analysis I need to do looks at the
interaction of time  and IV1, which has 2 levels.  I
created a  matrix using the following

Mat ymat = (1,0,-1\0,1,-1)

However the output was quite different from the output
from  SPSS Manova for the very same data and analysis.
Since I am more comfortable with SPSS, I  thought it
prudent to check my work before proceeding too far.

What should the matrix be to look at the time by
treatment interaction?

The reason I am not using SPSS to do these analyses is
that  Stata is better suited to my non-normal data.
(I ultimately plan to use the negative binomial option
on the Manova, once I get the bugs worked out.)

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