Axel,
you need a model for such type of analyses and coin is completely
model-free.
Torsten
On Mon, 23 Sep 2013, Axel Urbiz wrote:
Dear List,
I'm interested in performing a permutation test on the interaction between a
binary treatment
indicator and a covariate (either continuous or categorical). I'm interested in
the p-value
of the interaction effect from a permutation test, and I'm using the coin
package for that
purpose.
As I haven't seen any examples like this in the package documentation (or
anywhere else), I'm
not sure how to specify the test in this case. For example, should I interpret
the p-value in
the example below as the pvalue of the interaction effect between group and the
covariate x.
set.seed(1)
library("coin")
data("rotarod", package = "coin")
x <- rnorm(24)
rotarod <- cbind(rotarod, x)
pvalue(independence_test(time ~ group * x, data = rotarod))
Your advice would be much appreciated.
Regards,
Axel.
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