lecture 2 - Association Rules(Aka Affinity Analysis or...

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1 Association Rules (Aka Affinity Analysis or Market Basket Analysis) Prof. Tom Fomby Department of Economics Southern Methodist University Dallas, Texas 75275 July 2013 Association Rules represent an unsupervised learning method that attempts to capture associations between groups of items. Association Rules have also been referred to in the literature as Market Basket analysis or Affinity analysis. For example, consider the EXCEL file Associations.xls that details the transactions of individuals in a bookstore. The first 12 cases (out of 2000) taken from the Associations file are reproduced below in Table 1. Table 1 12 Bookstore Transactions In Binary Format ChildBks YouthBks CookBks DoItYBks RefBks ArtBks GeogBks ItalCook ItalAtlas ItalArt Florence 0 1 0 1 0 0 1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 0 1 0 1 0 0 0 0 0 0 1 0 0 0 1 0 0 0 0 1 0 0 0 0 1 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 1 0 0 1 0 0 0 0 0 0 1 0 0 1 0 0 0 0 0 0 0 1 1 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 The above reporting style is called Binary Format as compared to Item List Format as represented in Table 2 below where the first 5 transactions from a grocery store are recorded. Table 2 5 Grocery Store Transactions In Item List Format hering corned_b olives Ham turkey bourbon ice_crea baguette soda hering Cracker heineken olives corned_b avocado cracker artichok Heineken ham turkey sardines olives bourbon coke Turkey ice_crea ham peppers hering corned_b apples Olives steak avocado turkey
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2 More formally an item list is a set of items chosen during a given trip to a store while a transactions file is a data file that details the items purchased by customers during trips to the store. Therefore, the Associations.xls file in XLMINER is a transactions file, the first 12 transactions of which are listed in Table 1 above. The item list of the first transaction consists of {YouthBks, DoItYBks, GeogBks}. The question of interest here is the following: If items in group A appear in a market basket, what is the probability that items in group C will also be purchased? In probability terms, what is the conditional probability of C, given A, i.e. Pr(C|A)? Also we might ask , “I f the fact that group A items are in the market basket, does that condition at all the probability that the group C items will also be in the market basket? That is, is simply Pr(C|A) = Pr(C) and thus knowing that group A items are in the market has no effect on group C items being in the market basket? Suppose, for example, that a person in the bookstore has purchased an Italian Cookbook. What is the probability that the same person would also purchase a General Cookbook given that the Italian Cookbook is in the market basket? Is the purchase of the General Cookbook independent of the purchase of an Italian Cookbook? Which items in the bookstore are associated with or have an affinity for each other? Answering questions like the above is the task of Association Rules.
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  • Spring '08
  • TomFomby
  • Economics, Probability, The Rules, The Association, Association rule learning, Antecedent, Consequent

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