CMS Medicaid Data: Linking Mothers to Infants


This article summarizes two methods available to link mothers and their infants using the MAX data. Frequently researchers using the CMS Medicaid Analytic Extract (MAX) data are looking for ways to link mothers with their infants. Given the available identifiers in MAX data, there are two options.
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Option 1: Medicaid Case Identification Number

If a researcher is only working with MAX data, the only option is to use the Medicaid case identification number, El_State_Case_Num, in the MAX Personal Summary (PS) file. However, assignment of case IDs varies by state and within state by enrollment criteria such as eligibility group. All family members may not be found under the same case ID. The MAX Personal Summary file data dictionary notes that the ID may vary over time and that there can be single person cases.

Option 2: Birth Certificates

A second option is to link mothers and their infants by obtaining birth certificate data where the state records the mother’s SSN as well as the infant’s SSN on the infant birth certificate, which can then be cross-walked to MAX records that contain the SSNs of both mothers and infants. Researchers need to contact their states of interest to determine if birth certificate linkage is an option and what each state’s specific process is for data release. Since CMS also has requirements for data requests that include linking via an SSN, once researchers know how a state handles release of birth certificate data that includes SSNs, they should contact ResDAC to discuss options for linking to CMS MAX data.

The rate for successful linkage under either option will vary by state, eligibility group and possibly by year. Researchers planning to request data to link mothers and infants will need to specify the linkage strategy in their study protocol and are encouraged to work with both ResDAC and the involved states to manage issues such as encryption of identifiers in order to maximize the chances that a study is successful.