Mean predictive measure of association for surrogate splits in regression tree
ma = surrogateAssociation(tree)
ma = surrogateAssociation(tree,N)
returns a matrix of predictive measures of association for the predictors in
ma
= surrogateAssociation(tree
)tree
.
returns a matrix of predictive measures of association averaged over the nodes in vector
ma
= surrogateAssociation(tree
,N
)N
.

A regression tree constructed with 

Vector of node numbers in 


Element ma(i,j)
is the predictive measure
of association averaged over surrogate splits on predictor j
for
which predictor i
is the optimal split predictor.
This average is computed by summing positive values of the predictive
measure of association over optimal splits on predictor i
and
surrogate splits on predictor j
and dividing by
the total number of optimal splits on predictor i
,
including splits for which the predictive measure of association between
predictors i
and j
is negative.