A staff member at a medical research company is creating a query of patient data that is archived at a Health Maintenance Organization (HMO). The query includes patient’s social security numbers (SSN), which are querying as XXX-XX-1234, and dates of births (DOB), which are showing as XX-XX-1974. While the staff member would like to obtain the entire SSN and DOB, they are unable to reverse the queried data to view the entire data fields. Which de-identification method is being used by the HMO to protect the patient data?