Discovery of Hidden Correlations in a Local Transaction Database Based on Differences of Correlations

Given a transaction database as a global set of transactions and its sub-database regarded as a local one, we consider a pair of itemsets whose degrees of correlations are higher in the local database than in the global one. If they show high correlation in the local database, they are detectable by some search methods of previous studies. On the other hand, there exist another kind of paired itemsets such that they are not regarded as characteristic and cannot be found by the methods of previous studies but that their degrees of correlations become drastically higher by the conditioning to the local database. We pay much attention to the latter kind of paired itemsets, as such pairs of itemsets can be an implicit and hidden evidence showing that something particular to the local database occurs even though they are not yet realized as characteristic ones. From this viewpoint, we measure paired itemsets by a difference of two correlations before and after the conditioning to the local database, and define a notion of DC pairs whose degrees of differences of correlations are high. As the measure is non-monotonic, we present an algorithm, searching for DC pairs, with some new pruning rules for cutting off hopeless itemsets. We show by an experimental result that potentially significant DC pairs can be actually found for a given database and the algorithm successfully detects such DC pairs.