Usually 10-fold cross validation is performed more than once to get an
estimate of the misclassification rate thus I thought "number of
cross-validations" was different from the "number of cross-validation
groups". So, if I want to perform 10-fold cross-validation more than once
(say 5) in order to estimate the miscalssification rate I have to run
xpred.rpart 5 times ?
Thanks
Paolo
I have some problems in understanding the meaning of the xval argument in
the two functions rpart.control and xpred.rpart. In the former it is
defined
as the number of cross-validations while in the latter it is defined as
the
number of cross-validation groups.
It is the same thing. If xval=10 then the data is divided into 10
disjoint
groups. A model is fit with group 1 left out and that model is used to
predict
the observations in group 1; then a model is fit with group 2 left out;
then
group 3, ...
So 10 groups = 10 fits of the model.
Actually I thought that in rpart.control
Terry Therneau
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