The final rule permitting release of the newly available Part D data to researchers was issued in May 2008. In addition to usual protections for beneficiary privacy, this rule includes additional protections for commercially sensitive plan information. Since the initial release of Part D data, CMS has rolled out an increasing number of data elements and linkages, and is continuing to assemble supplemental data files.
Part D Event Data
outlines the available Part D research data files.10
The primary data source for Part D drug utilization is the Part D Event (PDE) files, which are currently available for 2006-2008. This file contains detailed information on each drug event for PDP and MAPD plan beneficiaries, and encrypted beneficiary, pharmacy, prescriber, and plan identifiers that allow linkage with other files, such as inpatient and outpatient claims data, and Part D plan characteristics files. The PDE contains information on each drug dispensed including the National Drug Code (NDC), the quantity dispensed, and days supply, allowing for the examination of therapy adherence and persistence based on dispensing data, which have been previously validated.11, 12
Part D Research Identifiable and Supplemental Data Files
The PDE data also capture cost data, such as total drug costs and patient payments. These data allow for examination of variation in spending patterns and cost of care analyses. The PDE data also specifies the benefit phase during which each drug was filled (e.g., deductible or initial coverage phase) based on the benefit structure implemented by each beneficiaries’ plan, which affects patients’ and payers’ costs. This file also includes plan-specific information on the formulary coverage for each drug dispensed, including the tier and utilization management requirements. Plan-level information on formulary and benefit structures can be valuable for identifying quasi-experiments or instrumental variables for statistical analyses.
Beneficiary Summary Files
PDE data can be linked with information on individual beneficiary characteristics. The Beneficiary Summary File contains beneficiary-level information on basic demographics, including age, gender, race, and geographic location. This file also describes beneficiaries’ months of enrollment in Parts A, B, C, and D, including the type of coverage (e.g., retiree, Part D stand-alone plan, Part D Medicare Advantage Plan), dual eligibility status, and whether they are receiving the Part D low income subsidy. The Beneficiary Annual Summary File contains additional information on patients’ inpatient diagnosis related groups, as well as two sets of chronic condition flags.
Supplemental Part D Files
CMS has rolled out an increasing number of data elements since the Part D data rule was originally issued that supplement the PDE and beneficiary data (). The Drug Characteristics File includes drug names (generic and brand) and strength and dosage form information by National Drug Code. Plan characteristics files can be linked to the PDE data using the encrypted plan identifier to examine detailed information on plan type, cost-sharing levels, premium information, and service area. The Pharmacy Characteristics File includes information on the type of pharmacy where beneficiaries filled their prescriptions. Lastly, the Prescriber Characteristics File contains information on the prescriber’s specialty, credentials and geographic location.
Medicare Part A and B Data
Part D data can also be linked to Traditional Medicare data on beneficiaries’ other medical claims (e.g., hospital, skilled nursing facility, hospice, physician). For example, the Inpatient Standard Analytic File includes claims for inpatient stays, including diagnosis and procedure codes (ICD-9), Diagnosis Related Groups (a classification system used for prospective Medicare payments), date, facility, and cost information. The Carrier file contains claims for non-institutional providers, largely physicians. It also contains diagnosis and procedure codes (ICD-9 and CMS Common Procedure Coding System (HCPCS) codes), reimbursement amounts, and provider identifiers.
Medicare Advantage (Part C) Data
Information at the beneficiary level on inpatient and outpatient services use and diagnoses within the Medicare Advantage program is not currently available to researchers. Monthly enrollment information is available in the Beneficiary Summary file so beneficiaries’ transitions between Traditional fee-for-service Medicare and Medicare Advantage can be tracked. Prior to the introduction of Part D, beneficiaries could switch between Traditional Medicare and Medicare Advantage plans monthly. In 2006, beneficiaries were restricted to switching only during the first six months of the year, and from 2007 onward, the first three months of the year.
Additional Linkable Datasets
Medicare claims data can also be linked with Medicaid data for dual-eligible beneficiaries, as well as datasets focused on specific subpopulations or collected via surveys, such as the SEER (Surveillance Epidemiology and End Results) Cancer Registry, Long Term Care Minimum Data Set (MDS), the Home Health Outcome and Assessment Information Set (OASIS), the Medicare Current Beneficiary Survey, and the Health and Retirement Survey. While the available sample size is more limited when linking to these data sources, they can provide a richer set of socio-demographic, health, and clinical characteristics than is available in the claims data alone.