Definition: association rule Association rule TD tems An implication expression of the form X.. where x and y are itemsets Bread. milk Bread, Diaper, Beer, eggs Example: {Mik, Diaper}→{Ber 2345 Milk, Diaper, Beer, Coke Bread, Milk, Diaper, Beer Bread, Milk, Diaper, Coke Rule evaluation metrics Support (s) e fraction of transactions that contain Example both x and y Mik, Diaper}→Beer Confidence(c) e Measures how often items in y o Milk, Diaper, Beer)2 =0.4 appear in transactions that T contain x C O(Milk, Di Diaper, Beer) 2 0.67 o Milk, Diaper) 3 n Steinbach. Kumar Introduction to Data Mining 4/18/2004© Tan,Steinbach, Kumar Introduction to Data Mining 4/18/2004 ‹#› Definition: Association Rule Example: {Milk ,Diaper } Beer 0.4 5 2 | T | (Milk,Diaper,Beer) = = =  s 0.67 3 2 (Milk,Diaper) (Milk,Diaper,Beer) = = =   c Association Rule – An implication expression of the form X → Y, where X and Y are itemsets – Example: {Milk, Diaper} → {Beer} Rule Evaluation Metrics – Support (s) ◆ Fraction of transactions that contain both X and Y – Confidence (c) ◆ Measures how often items in Y appear in transactions that contain X TID Items 1 Bread, Milk 2 Bread, Diaper, Beer, Eggs 3 Milk, Diaper, Beer, Coke 4 Bread, Milk, Diaper, Beer 5 Bread, Milk, Diaper, Coke