In this election season, when tackling health care costs is a top voter concern, the Democratic primary candidates are offering different visions for reform, and have spent debates arguing over the costs of those plans. What has gotten less attention, and what is at the heart of any reform, is the biggest factor in health care spending: hospital payments.

“If we want to control the health care burden on the U.S. economy, then we have to control hospital prices,” said Gerald Friedman, an economics professor at the University of Massachusetts, Amherst who studies health care financing.

Proposed changes to hospital payments are buried in plans to overhaul health care by moving to "Medicare for All” or the more moderate public option, sometimes called "Medicare for All Who Want It." Both would rock the books of every hospital in Massachusetts because Medicare almost always pays hospitals less than private health insurance companies. Sometimes a lot less.

“There would be a redistribution of payments,” said Meredith Rosenthal, a professor of health economics and policy at Harvard’s Chan School of Public Health. “That’s the big change. Some hospitals would be winners and others would be losers.”

Among the possible “winners” under “Medicare for All”: Cambridge Health Alliance, the only hospital in Massachusetts that made more money treating an elderly Medicare patient than a younger person with private insurance. That’s based on 2016 data — the latest available — used by the Health Policy Commission (HPC) for a report that compares average discharge payments to hospitals from Medicare versus private health plans.

Cambridge is the only hospital in Massachusetts that would have received more money in 2016 if all payments were based on Medicare rates. Cambridge, a safety net hospital, is one of a few hospitals that provide mental health care and other services with low reimbursement rates. Health economists say these hospitals and their low- to moderate-income patients could benefit under a shift to more Medicare payments.

“Losers” might include some of the state’s largest and most expensive hospitals, like Massachusetts General — which made 175% of its Medicare rate for an average private insurance patient discharge — and those that can demand higher payments because they serve a specific area, like Cape Cod Hospital, which made 208% for private insurance patients over Medicare. For these hospitals, Rosenthal says the worry is they would cut back or end high-tech services “or reduce quality in terms of staffing.”

But in reality no one knows what would be lost in a move to “Medicare for All,” said Stuart Altman, a health policy professor at Brandeis University who chairs the HPC. Would hospitals trim spending on research, training, salaries or amenities? How would that affect patient care?

“Once you’ve developed a lifestyle based on a certain income, to say that you could live with 20% less doesn’t mean you won’t have to give up a lot," said Altman. “And maybe what you give up is quite important.”