1. A method for detecting fraud in health care transactions, the method being implemented by one or more data processors and comprising: receiving, by at least one data processor, a transaction record, the transaction record characterizing at least one service provided to a client by a provider on a date; for each service in the transaction record: determining, by at least one data processor, 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, by at least one data processor, 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, by at least one data processor, that the transaction is potentially fraudulent.