the beer and diapers story one of the stories that is often mentioned in the context of basket analysis is the "diapers and beerstory it states that when supermarkets first started to look at their datathey found that diapers were often bought together with beer supposedlyit was the father who would go out to the supermarket to buy diapers and then would pick up some beer as well there has been much discussion of whether this is true or just an urban myth in this caseit seems that it is true in the early sosco drug did discover that in the early evening beer and diapers were bought togetherand it did surprise the managers who haduntil thennever considered these two products to be similar what is not true is that this led the store to move the beer display closer to the diaper section alsowe have no idea whether it was really that fathers were buying beer and diapers together more than mothers (or grandparentsobtaining useful predictions it is not just "customers who bought also bought "even though that is how many online retailers phrase it (see the amazon com screenshot given earlier) real system cannot work like this why notbecause such system would get fooled by very frequently bought items and would simply recommend that which is popular without any personalization for exampleat supermarketmany customers buy bread (say percent of customers buy breadso if you focus on any particular itemsay dishwasher soapand look at what is frequently bought with dishwasher soapyou might find that bread is frequently bought with soap in fact percent of the times someone buys dishwasher soapthey buy bread howeverbread is frequently bought with anything else just because everybody buys bread very often what we are really looking for is customers who bought are statistically more likely to buy than the baseline so if you buy dishwasher soapyou are likely to buy breadbut not more so than the baseline similarlya bookstore that simply recommended bestsellers no matter which books you had already bought would not be doing good job of personalizing recommendations analyzing supermarket shopping baskets as an examplewe will look at dataset consisting of anonymous transactions at supermarket in belgium this dataset was made available by tom brijs at hasselt university the data is anonymousso we only have number for each product and basket that is set of numbers the datafile is available from several online sources (including the book' companion websiteas retail dat