1. An apparatus, comprising: an interface configured to receive an identifier of a first index attribute and a second index attribute; and a processor in data communication with the interface, the processor configured to: search the database for a first group of healthcare records associated with the first index attribute; assign a first distinguishing identifier to each healthcare record in a subset of the first group of healthcare records in response to a determination that the subset of healthcare records have a common value of a second index attribute; search the database for a second group of cohort healthcare records, wherein each cohort healthcare record in the second group of cohort healthcare records shares a common second index attribute with a healthcare record in the first group of healthcare records, but not associated with the first index attribute; assign a second distinguishing identifier to each cohort record in the second group of cohort healthcare records that corresponds to the first distinguishing identifier assigned to a healthcare record in the subset of the first group of healthcare records; and calculate a statistic in response to healthcare information associated with the first group of healthcare records and the second group of cohort healthcare records based on the assigned first and second identifiers, wherein the statistic comprises a probability of an attribute shared between a diagnosis for a person represented by a healthcare record in the second group and a diagnosis for a person represented by a healthcare record in the first group.