14. A computer system for detecting associations between items represented in a data repository, the system comprising: a probabilistic analysis component comprising computer hardware, the probabilistic analysis component configured to: access user data comprising information about item selections by a plurality of users; and programmatically generate associations between first and second items based at least in part on the user data by at least: determining, from the user data, a first probability that first users selected both the first and second items, estimating, from the user data, a second probability that second users who selected the first item would have selected the second item based at least partly on a number of item selections other than the selection of the first item made by each of the second users, deriving an association score for the first and second items based at least in part on the first and second probabilities, the association score reflecting a degree of the association between the first and second items, and store the association in a data repository.
14. A computer system for detecting associations between items represented in a data repository, the system comprising: a probabilistic analysis component comprising computer hardware, the probabilistic analysis component configured to: access user data comprising information about item selections by a plurality of users; and programmatically generate associations between first and second items based at least in part on the user data by at least: determining, from the user data, a first probability that first users selected both the first and second items, estimating, from the user data, a second probability that second users who selected the first item would have selected the second item based at least partly on a number of item selections other than the selection of the first item made by each of the second users, deriving an association score for the first and second items based at least in part on the first and second probabilities, the association score reflecting a degree of the association between the first and second items, and store the association in a data repository. 15. The system of claim 14 , wherein the items comprise items in an electronic catalog.