Bagging is a variance reduction method for model building. That is,
through building multiple models from samples of the training data,
the aim is to reduce the variance. Bagging
is a technique
generating multiple training sets by sampling with replacement from
the available training data. In an ideal world we can eliminate
variance due to a particular choice of training set by combining
models that are built from each training set of size N. In practise
only one training set is available. By sampling with replacement from
the training set to form new training sets, bagging simulates the
ideal situation. Bagging is also known as
bootstrap aggregating. See
See Chapter 13.1