interact.gbm {gbm}R Documentation

Estimate the strength of interaction effects

Description

Computes Friedman's H-statistic to assess the strength of variable interactions.

Usage

interact.gbm(x,
             data,
             i.var = 1,
             n.trees = x$n.trees)

Arguments

x

a gbm.object fitted using a call to gbm

data

the dataset used to construct x. If the original dataset is large, a random subsample may be used to accelerate the computation in interact.gbm

i.var

a vector of indices or the names of the variables for compute the interaction effect. If using indices, the variables are indexed in the same order that they appear in the initial gbm formula.

n.trees

the number of trees used to generate the plot. Only the first n.trees trees will be used

Details

interact.gbm computes Friedman's H-statistic to assess the relative strength of interaction effects in non-linear models. H is on the scale of [0-1] with higher values indicating larger interaction effects. To connect to a more familiar measure, if x_1 and x_2 are uncorrelated covariates with mean 0 and variance 1 and the model is of the form

y=β_0+β_1x_1+β_2x_2+β_3x_3

then

H=\frac{β_3}{√{β_1^2+β_2^2+β_3^2}}

Value

Returns the value of H.

Author(s)

Greg Ridgeway gregr@rand.org

References

J.H. Friedman and B.E. Popescu (2005). “Predictive Learning via Rule Ensembles.” Section 8.1

See Also

gbm, gbm.object


[Package gbm version 1.6-3.1 Index]