As of 2023, about half of all Medicare beneficiaries were enrolled in Medicare Advantage (Biniek et al 2023)—approximately 30.8 million people (Ochieng et al 2023). Medicare Advantage is a private managed care alternative to the traditional fee-for-service Medicare. With Medicare Advantage, healthcare organizations receive a set amount of money to cover the healthcare costs of enrolled patients, and the amount is determined by the patient's risk score, which is based on patient characteristics and health conditions (Centers for Medicare & Medicaid Services 2024). Thus, Medicare Advantage plans have different incentives to document diagnoses for patients than fee-for-service plans, as diagnoses are linked to risk scores, which could lead to aggressive coding practices (Keating 2023). These differences can impact the reliability and relevance of the data used for PCTs.

Some important differences have been highlighted in examples from the literature, including differences in population, medication, preventive services, and across states and counties.

• Population
  • Medicare Advantage plans include a higher share of members who require chronic disease management, and those with serious mental health conditions or substance abuse issues (Waddill 2021).
• Medication use
  • Use of high-risk medications that should be avoided in older adults were lower in Medicare Advantage patients (Figueroa et al 2023).
• Preventative services
  • Medicare Advantage plans are incentivized to enhance preventive services, such as screenings, including higher mammogram rates in older patients with dementia (Raver et al 2024).
  • Lung cancer screening is higher in patients who have Medicare Advantage (Hughes et al 2023).
• Variation across states and counties
  • There is wide variation in enrollment rates across states and counties, which could be reflective of urban vs rural populations, the number of Medicare beneficiaries and their healthcare use patterns, and differences in the firms that offer Medicare Advantage across different geographic regions (Ochieng et al 2023).

Researchers should be aware that differences in the data from Medicare Advantage or fee-for-service Medicare claims could be reflective of a true pattern, an artifact of billing, enrolled population, or treatments and medications.

Finally, trials that include both Medicare Advantage and fee-for-service Medicare populations would need to purchase both sets of data, which can be expensive depending on the number of years of data needed. The alternative to purchasing both sets of data is to push trial data into the Virtual Research Data Center and pay a flat fee for access to both, which comes with some logistical challenges but is worth considering.