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convex hull of subgroups induced using the quality measure qq TP/(FP + g) at data stage B. Labels B1 and B2 denote positions of subgroups selected by the medical expert, and X1 and X2 two of the seven subgroups forming the TP/FP convex hull.

Figure 5: The same subgroups as in Figure 4 shown in the ROC space instead of the TP/FP space. The equivalence of these two spaces can be easily noticed.

In the ROC space a thin line connecting points (0,0) and (100,100) represents rule positions with significance equal zero.
Statistical differences in distributions for all the descriptors (attributes) between these two populations is tested using the χ 2 test with 95% confidence stage ( p = 0.05). For this purpose numerical attributes have been partitioned in up to 30 intervals so that in every interval there are at least 5 instances. Among the attributes with significantly different distributions there are always those that form the features describing the subgroups (the principal factors), but usually there are also other attributes with significantly different value distributions. These attributes are called supporting attributes, and the features formed of their values that are characteristic for the discovered subgroups are called supporting factors.