Hi Henk,
Sorry, my mistake. The F1 and F2 contrasts have just the first two
lines, i.e.,
F1:
1 0 0 0 0 0
0 1 0 0 0 0
F2:
0 0 0 1 0 0
0 0 0 0 1 0
otherwise of course not only the mean enters in the stat, but also it
affects the rank of the contrast.
I'll be back later to comment on the other points.
All the best,
Andersn
Am 26.02.14 08:02, schrieb H van Steenbergen:
> Thanks a lot, Anderson. If I understand your new factor-effect model correctly it is identical to the one I proposed for the group with three levels, except that I: a) already included a demeaned covariate; b) used a different order of EVs; and c) did not describe the additional t-tests in case one wants to get cell means.
>
> Wrt to the t-tests and F-tests you described: the t-tests seems to get the cell means of the three levels groups and the three slopes (of the covariate) in these three groups. However, I am not sure about the F-test. When using the factor-effect approach you usually only includes K-1 contrasts for the F-test. I want to be explicit about this because other users may use the information posted here as well.
>
> So with your model (COV still needs to be demeaned first, and columns 4 and 5 updated accordingly):
>
> A2-Mn A3-Mn Mean A2-Mn*COV A3-Mn*COV COV
> -1 -1 1 -0.6299 -0.6299 0.6299
> -1 -1 1 -0.032 -0.032 0.032
> -1 -1 1 -0.6147 -0.6147 0.6147
> -1 -1 1 -0.3624 -0.3624 0.3624
> 1 0 1 0.0495 0 0.0495
> 1 0 1 0.4896 0 0.4896
> 1 0 1 0.1925 0 0.1925
> 1 0 1 0.1231 0 0.1231
> 1 0 1 0.2055 0 0.2055
> 0 1 1 0 0.1465 0.1465
> 0 1 1 0 0.1891 0.1891
> 0 1 1 0 0.0427 0.0427
> 0 1 1 0 0.6352 0.6352
>
> would it not be better to use the following t-tests (I have renumbered your t-test into C7..C12)?
>
> C1: 1 0 0 0 0 0
> C2: 0 1 0 0 0 0
> C3: 0 0 1 0 0 0
> C4: 0 0 0 1 0 0
> C5: 0 0 0 0 1 0
> C6: 0 0 0 0 0 1
> C7: -1 -1 1 0 0 0
> C8: 1 0 1 0 0 0
> C9: 0 1 1 0 0 0
> C10: 0 0 0 -1 -1 1
> C11: 0 0 0 1 0 1
> C12: 0 0 0 0 1 1
>
> and the following F-tests?
>
> F1-MainA 1 1 0 0 0 0 0 0 0 0 0 0
> F2-MainCOV 0 0 0 0 0 1 0 0 0 0 0 0
> F3-AxCOV 0 0 0 1 1 0 0 0 0 0 0 0
>
> In addition, you indicated that the original two-group model was rank deficient even though I was using the factor-effects approach. Given that randomise did not complain about rank-deficiency of the two-group x covariate model mentioned earlier, I was wondering whether there is an easy way to determine whether a model is rank deficient (e.g. in SPSS or matlab)?
>
> Thanks for your help!
>
> Best, Henk
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