Various rule evaluation measures and heuristics have been studied for
subgroup discovery, aimed at balancing the size of a group (referred
to as factor *g* by Klosgen1996) with its distributional
unusualness (referred to as factor *p*). The properties of functions
that combine these two factors have been extensively studied (the
so-called ``*p*-*g*-space'').

Similarly, the weighted relative accuracy heuristic, defined as
and used by tod:fla:lav:2000, trades off generality of the
rule (*p*(*Cond*), i.e., rule coverage) and relative accuracy

*p*(*Class*|Cond) - *p*(*Class*). This heuristic is a reformulation of one
of the measures used in EXPLORA.

Besides such `objective' measures of interestingness, some `subjective' measure of interestingness of discovered patterns can be taken into the account, such as actionability (`a pattern is interesting if the user can do something with it to his or her advantage') and unexpectedness (``a pattern is interesting to the user if it is surprising to the user'') ( Silberschatz & Tuzhilin, 1995).