A matrix or data.frame of training data predictors.
newX
A test set of predictors.
family
Not used by the function directly, but ensures compatibility
with SuperLearner.
obsWeights
Not used by the function directly, but ensures
compatibility with SuperLearner.
rangeThresh
If the the range of the outcomes is smaller than this
number, the method returns the empirical average of the outcomes. Used for
computational expediency and stability.