A new analysis of the Patient Protection and Affordable Care Act shows the law of supply and demand at work. Enrollment through exchanges drops significantly as income rises, according to Avalere Health, an advisory company in Washington, D.C.

"People receiving more-generous subsidies are expected to enroll in the exchanges at higher rates," said Elizabeth Carpenter, director at Avalere. "However, participation levels decline as incomes increase, even among individuals who would be eligible for both premium subsidies and cost-sharing reductions."

The analysis reviewed Department of Health and Human Services reported income distribution for the 2015 exchange population in the 37 states using HealthCare.gov.