1. A computer-implemented method of determining an item to recommend, the computer-implemented method comprising: detecting a behavior-based association between a first item facet and a second item facet based on selections by users of catalog items in an electronic catalog, wherein a first plurality of the catalog items have the first item facet and a second plurality of the catalog items have the second item facet the first item facet comprising a first attribute shared among a first plurality of items, and the second item facet comprising a second attribute shared among a second plurality of items, the second attribute differing from the first attribute; identifying a first catalog item having the first item facet; determining a plurality of recommendation rules for the first catalog item, wherein performance of different recommendation rules of the plurality of recommendation rules results in identification of different sets of items for recommendation to users who access the first catalog item; scoring each of the plurality of recommendation rules to obtain a score for each recommendation rule, the score generated based at least in part on a ratio of posterior odds to prior odds determined from historical item-access data associated with the recommendation rule; classifying the plurality of recommendation rules based at least in part on a determination of whether the score associated with each of the recommendation rules satisfies a score threshold to obtain a first set of recommendation rules that satisfy the score threshold and a second set of recommendation rules that do not satisfy the score threshold, wherein the first set of recommendation rules comprise positive recommendation rules and the second set of recommendation rules comprise negative recommendation rules; receiving additional item-access data associated with at least one recommendation rule from the second set of recommendation rules; rescoring the at least one recommendation rule based on the additional item-access data to obtain an updated score; reclassifying the at least one recommendation rule based at least in part on a determination that the updated score satisfies the score threshold, wherein reclassifying the at least one recommendation rule comprises removing the at least one recommendation rule from the second set of recommendation rules and adding the at least one recommendation rule to the first set of recommendation rules; selecting a recommendation rule from the first set of recommendation rules based at least in part on the score associated with the recommendation rule; selecting, using the selected recommendation rule and based at least partly on the behavior-based association between the first and second item facets, a second catalog item to recommend to users who select the first catalog item, said second catalog item having the second facet; and outputting for recommendation the second catalog item to a user who selected the first catalog item, wherein the computer-implemented method is performed programmatically by a computing system comprising one or more computing devices.