13. The system of claim 9 , wherein determining the likelihood for the service to be repeated given the time interval further comprises: for each of a plurality of time intervals, using historical data from a plurality of transactions to determine a likelihood with which the service is repeated during the interval.
9. A system for detecting fraud in health care transactions comprising: at least one data processor; and memory coupled to the at least one data processor, the memory storing instructions, which when executed, cause the at least one processor to perform operations comprising: receiving a transaction record; for each service in the transaction record, the transaction record characterizing at least one service provided to a client by a provider on a date: determining a time interval between the date the service was provided to the client, and a date the same service was previously provided to the client; determining a likelihood for the service to be repeated given the time interval using co-occurrence data based on a vector space modeling of historical service co-occurrence in which performed service codes are represented in a vector space derived from a statistical distribution of service codes in reimbursement claims; and responsive to the likelihood exceeding a first threshold, indicating that the transaction is potentially fraudulent.