Long-term trends in the concentration of Medicare spending.

Medicare spending is concentrated among a few high-cost beneficiaries who are often targeted by cost-saving interventions. The Continuous Medicare History Sample file was used to analyze trends in the spending concentration over thirty years. Annual expenditures became less concentrated over time, although the year-to-year persistence of person-level high costs remained strong. There was an increase in the prevalence of chronic conditions among high-cost beneficiaries, which supports the rationale for focusing cost-saving interventions on chronic disease management. However, the decrease in concentration may reduce the potential savings from interventions focused on such beneficiaries.