Rand's study found that a total of more than 9.6 million people would leave the individual health insurance rolls in 34 states served by HealthCare.gov, the federal Obamacare exchange, if the Supreme Court rules subsidies issued through that marketplace are illegal under the Affordable Care Act.
Without such subsidies, many people would find their monthly premiums unaffordable.
"This decline includes plans sold in the [government-run Obamacare] marketplaces and those sold outside of the marketplaces that comply with ACA," the study said.
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Rand also projected that individual insurance premiums in those states would leap by 47 percent if the subsidies are yanked by a high court decision. Rand cited as an example a jump that would translate into a 40-year-old nonsmoker enrolled in a so-called silver plan paying an extra $1,610 in premium payments annually.
The estimated price increase stems from the fact that many people, particularly the younger and healthier, would stop buying insurance if they no longer received subsidies through HealthCare.gov, leaving a disproportionate of older, sicker enrollees in the plans, and using health benefits.
"The departure of young and healthy people from the health insurance market would cause premiums to rise further, leading to a cycle of additional departures and further premium increases," the study said.
Christine Eibner, a Rand senior economist and the study's senior author, said, "The disruption would cause significant instability and threaten the viability of the individual health insurance market in the states involved."
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"Our analysis confirms just how much the subsidies are an essential component to the functioning of the ACA-compliant individual market," Eibner said.