Rules for Contrast Sets Paulo J. Azevedo ∗ CCTC, Departamento de Inform´atica Campus de Gualtar Universidade do Minho 4710-057 Braga Portugal pja@di.uminho.pt Abstract In this paper we present a technique to derive rules describing con- trast sets. Contrast sets are a formalism to represent groups differ- ences. We propose a novel approach to describe directional contrasts using rules where the contrasting effect is partitioned into pairs of groups. Our approach makes use of a directional Fisher Exact Test to find significant differences across groups. We used a Bonferroni within- search adjustment to control type I errors and a pruning technique to prevent derivation of non significant contrast set specializations. Keywords: Contrast Sets, Association Rules, Fisher exact Test, Bonferroni Adjustment * This work was Supported by Funda¸c˜ ao Ciˆ encia e Tecnologia, Project PFound, Project ProtUnf, FEDER and Programa de Financiamento Plurianual de Unidades de I & D. 1