Nine in 10 Massachusetts seniors would have paid higher health insurance premiums in 2010 under a reformed Medicare structure similar to what Mitt Romney and Paul Ryan have proposed, according to a study published on Monday by the Kaiser Family Foundation.

Nationwide, 59 percent of Medicare enrollees would have faced higher out-of-pocket costs.

The analysis was based on actual health plan bids and Medicare costs in 2010, the most recent year for which complete data were available.

Advertisement - Continue Reading Below

The reform studied by Kaiser was similar, but not identical, to a proposal Ryan included in his 2013 budget. It featured premium support payments that seniors would use to purchase private health insurance in lieu of traditional, fee-for-service Medicare. Seniors would retain the right to enroll in the traditional Medicare program.

The per-capita value of the premium support payments was set by the cost of the second-cheapest private plan or traditional Medicare, whichever was less expensive to the government in any geographical region.

In these ways, the reforms studied by Kaiser mirrored Ryan’s proposal, which Romney has said is almost the same as his own.

Kaiser found that in Massachusetts, where health insurance is more expensive than the national average, a majority of seniors enrolled in Medicare in 2010 would have had to pay at least an extra $50 per month for the same coverage in the reformed program. Under the current Medicare system, beneficiaries generally pay the same premiums regardless of where they live.

President Obama’s reelection campaign posted a link to the report on its website, using the study as evidence to support its claim that the Romney-Ryan Medicare plan would prove costly for seniors.

But the study authors cautioned that their work “should not ... be interpreted as an analysis of any particular proposal, including the Romney-Ryan proposal, because such an analysis would require additional, more detailed policy specifications than are currently available and would also require assumptions about future shifts in demographics, spending and enrollment, nationally and by local markets, which would occur regardless of policy changes.”

Unlike the Romney-Ryan proposal, the plan studied by Kaiser assumed immediate, full participation by all Medicare enrollees. Romney and Ryan would phase in their premium support system gradually, beginning with new enrollees in 2023.

The Romney campaign emphasized that the Kaiser report was not a direct examination of the Republican ticket’s Medicare proposal.

“As the authors stress, this is not a study of the Romney-Ryan plan,” Romney spokeswoman Andrea Saul said in a statement. “Our plan would always provide future beneficiaries guaranteed coverage options with no increase in out-of-pocket costs from today’s Medicare.”