Skotara wrote:
Thank you for your help!
Sorry, for bothering you again..
I still have trouble combining within and between subject factors.
Interactions of within factors and D having only 2 levels work well.
How can I get the main effect of D? I have tried anova(mlmfitD, mlmfit).
With D having 3 levels I would expect the dfs to be 2 and 33. However,
the output states 84,24??
That's not a main effect, it's a simultaneous test of all 28 components.
What you need is an analysis of the average of all
within-measurements. In principle that is obtained by X=~0, M=~1 or
T=matrix(1,1,28) but there's a bug that prevents it from working (fixed
in R-patched a couple of days ago).
As long as the between factor has only 2 levels the between/within
interactions fit well with SPSS, but if D has 3 levels, the mismatch is
immense.
If I calculate the within effects with myma having not 12 subjects from
one group but for example 24 from 2 groups, the output treats it as if
all subjects came from the same group, for example for main effect A the
dfs are 1 and 35. SPSS puts out 1 and 33 which is what I would have
expected.. ..
Hmm, there's a generic problem in that you can't get some of the
traditional ANOVA table F tests by comparing two models, and in your
case, SPSS is de facto using the residuals from a model with A:D
interaction when testing for A. It might help if you try
anova(mlmfitD, X=~..., M=~...)
Look at the (Intercept) line.
Peter Dalgaard schrieb:
Nils Skotara wrote:
Thank you, this helped me a lot!
All within effects and interactions work well!
Sorry, but I still could not get how to include the between factor..
If I include D with 2 levels, then myma is 24 by 28. (another 12 by
28 for the
second group of subjects.)
mlmfitD <- lm(myma~D) is no problem, but whatever I tried afterwards
did not seem logical to me.
I am afraid I do not understand how to include the between factor. I
cannot include ~D into M or X because it has length 24 whereas the other
factors have 28...
Just do the same as before, but comparing mlmfitD to mlmfit:
anova(mlmfitD, mlmfit, X=~A+B, M=~A+B+C)
# or anova(mlmfitD, mlmfit, X=~1, M=~C), as long as things are balanced
gives the D:C interaction test (by testing whether the C contrasts
depend on D). The four-factor interaction is
anova(mlmfitD, mlmfit, X=~(A+B+C)^2, M=~A*B*C)
Zitat von Peter Dalgaard <[EMAIL PROTECTED]>:
Skotara wrote:
Dear Mr. Daalgard.
thank you very much for your reply, it helped me to progress a bit.
The following works fine:
dd <- expand.grid(C = 1:7, B= c("r", "l"), A= c("c", "f"))
myma <- as.matrix(myma) #myma is a 12 by 28 list
mlmfit <- lm(myma~1)
mlmfit0 <- update(mlmfit, ~0)
anova(mlmfit, mlmfit0, X= ~C+B, M = ~A+C+B, idata = dd,
test="Spherical"), which tests the main effect of A.
anova(mlmfit, mlmfit0, X= ~A+C, M = ~A+C+B, idata = dd,
test="Spherical"), which tests the main effect of B.
However, I can not figure out how this works for the other effects.
If I try:
anova(mlmfit, mlmfit0, X= ~A+B, M = ~A+C+B, idata = dd,
test="Spherical")
I get:
Fehler in function (object, ..., test = c("Pillai", "Wilks",
"Hotelling-Lawley", :
residuals have rank 1 < 4
dd$C is not a factor with that construction. It works for me after
dd$C <- factor(dd$C)
(The other message is nasty, though. It's slightly different in
R-patched:
> anova(mlmfit, mlmfit0, X= ~A+B, M = ~A+C+B, idata = dd,
test="Spherical")
Error in solve.default(Psi, B) :
system is computationally singular: reciprocal condition number =
2.17955e-34
but it shouldn't happen...
Looks like it is a failure of the internal Thin.row function. Ick!
)
I also don't know how I can calculate the various interactions..
My read is I should change the second argument mlmfit0, too, but I
can't
figure out how...
The "within" interactions should be straightforward, e.g.
M=~A*B*C
X=~A*B*C-A:B:C
etc.
The within/between interactions are otained from the similar tests of
the between factor(s)
e.g.
mlmfitD <- lm(myma~D)
and then
anova(mlmfitD, mlmfit,....)
--
O__ ---- Peter Dalgaard Øster Farimagsgade 5, Entr.B
c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K
(*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918
~~~~~~~~~~ - ([EMAIL PROTECTED]) FAX: (+45) 35327907
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