Since the classifiers of the combination scheme have a tendency of being naturally biased towards classifying the examples as negative, we assume that a classifier making too many positive decision is probably doing so unreliably.
15 Finally, the data set was divided into 10 concept learning problems where each problem consisted of a positive class containing 100 examples sampled from a single top 10 Reuters topic class and a negative class containing the union of all the examples contained in the other 9 top 10 Reuters classes.