Abstract: A classifier for determining whether an instance belongs to a particular class of instances of a plurality of classes, the classifier comprising: a plurality of first classifiers that operate on an instance to provide an indication as to which class the instance belongs, each of which classifiers is trained on a different subset of training instances from a same set of training instances wherein each training subset comprises a group of training instances that share at least one characteristic trait and different subsets have a different at least one characteristic trait; and a second classifier that operates on the indications provided by the first classifiers to provide an indication as to which class the instance belongs.