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st: Re: Anova and contrasts
I am having a problem with contrast following this anova:
.. anova eff system material immerse system*material system*immerse
material*immerse system*material*immerse if material>0
Number of obs = 180 R-squared =
0.5815
Root MSE = .036934 Adj R-squared =
0.5376
Source | Partial SS df MS F Prob >
F
------------------------+----------------------------------------------------
Model | .307109453 17 .018065262 13.24
0.0000
|
system | .027877154 4 .006969288 5.11
0.0007
material | .195840007 1 .195840007 143.56
0.0000
immerse | .000765629 1 .000765629 0.56
0.4548
system*material | .02563412 4 .00640853 4.70
0.0013
system*immerse | .02743688 3 .009145627 6.70
0.0003
material*immerse | .013875634 1 .013875634 10.17
0.0017
system*material*immerse | .025326868 3 .008442289 6.19
0.0005
|
Residual | .22099014 162 .001364137
------------------------+----------------------------------------------------
Total | .528099592 179 .002950277
I am interested in looking at the system*material interactions in more
detail. I have carried out "all possible" comparisons using:
.. test _coef[system[1]*material[1]]=_coef[system[1]*material[2]]
etc.
It occurs to me that I should setup a contrast matrix test this using the
mtestand allow for multiple testing. The problem is that the design matrix
has 54 columns. Do I need to set up this matrix for the 4 comparisons that I
need or is there a more efficient (or simpler) approach.
Many thanks.
Janet
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