Ways to make predictors differ
• Rely on the learning algorithm getting stuck in a different
local optimum on each run.
– A dubious hack unworthy of a true computer scientist
(but definitely worth a try).
• Use lots of different kinds of models:
– Different architectures
– Different learning algorithms.
• Use different training data for each model:
– Bagging: Resample (with replacement) from the
training set:  a,b,c,d,e  -> a c c d d
– Boosting: Fit models one at a time. Re-weight each
training case by how badly it is predicted by the
models already fitted.
• This makes efficient use of computer time because it does
not bother to “back-fit” models that were fitted earlier.