There’s no question that the fate of Obamacare is a matter of life and death.

The GOP’s senate plan to repeal and replace the Affordable Care Act, the Better Care Reconciliation Act, will result in 22 million fewer people with health insurance by 2026 compared to Obamacare, according to the non-partisan Congressional Budget Office. That’s like taking health coverage away from a country as big as Australia.

If the plan passes through the Senate and becomes law, health researcher and writer Atul Gawande told Vox, “There will be deaths.”

But getting a firm number on exactly how many deaths an ACA repeal would lead to is surprisingly contentious.

We don’t have any direct evidence of Obamacare’s impact on mortality, since it takes a long time for changes in things like health insurance to show up in death statistics, and the law was only enacted in 2009, as I’ve explained in a summary of the science on health insurance and mortality. (Studies looking at whether the ACA improved people’s health status and access to health care have had positive results, which suggests it should increase longevity.)

We do have something else though: very high-quality studies on the impacts of health insurance on mortality, which come to some pretty clear estimates. This research suggests that we would see more than 24,000 extra deaths per year in the US if 20 million people lost their coverage. And 20 million is less than the 22 million Americans the CBO expects will lose insurance by 2026. So the death toll from the GOP’s Obamacare repeal and replacement plan could be even higher.

The best studies on health insurance and mortality suggest 24,000 extra deaths per year if 20 million people lose their health insurance

There are two main types of studies that can tell us something about the effect repealing and replacing the ACA might have on mortality in America: First, there are simple non-randomized observational studies that use large health data sets to compare mortality rates between people who have had health insurance (government or employer-sponsored) and people who have not. Second, there are quasi-experimental studies, a stronger type of observational study design, which compare states that have expanded health insurance with those states that haven’t in a natural experiment.

The simple observational studies have come to pretty mixed conclusions. (You can read more about them here.) So I’ll focus on the higher-quality research on insurance and mortality.

To talk about that research, we have to understand how Medicaid has changed in America in recent years. Traditionally, Medicaid covered only low-income children, parents, and pregnant or disabled people. Over the past 10 years, several states expanded Medicaid coverage to include non-disabled adults who don’t have children — a group that is similar to the population that gained eligibility under Obamacare.

But Medicaid expansion has not been spread evenly throughout the US, and the Supreme Court ruled it was an optional feature of the ACA in 2012. This was clearly a loss for poorer Americans but it was a win for science: It led to a series of natural experiments across the country, in which researchers have compared the mortality rates in places that expanded coverage with the rates in places that didn’t.

The researchers behind this 2012 New England Journal of Medicine study took advantage of that variation: They compared what happened to health in three states (New York, Maine, and Arizona) that expanded Medicaid eligibility since 2000 to neighboring states without expansions, covering a period of five years before and five years after each state's expansion. They found mortality declined in places that expanded Medicaid by 20 deaths per 100,000, unlike neighboring states that didn’t expand Medicaid. Extrapolating that to the estimated 20 million who could lose health insurance with an ACA repeal, other researchers have suggested this would translate to 43,956 deaths in the US per year .

. Massachusetts has also offered a natural experiment for researchers who want to understand the impact of expanding health insurance on mortality rates. The state underwent a health reform in 2006 with the goal of providing insurance to almost all of its residents — and it became the model for the ACA. The best paper on this, published in 2014 in the Annals of Internal Medicine, compared the mortality rates in Massachusetts counties from 2001 to 2005 (before health reform expanded insurance) and 2007 to 2010 (after health reforms) to changes in control counties with similar demographic and economic conditions. Here, they found that the health insurance expansion prevented 320 deaths per year since it began in 2006. If that pattern holds for the ACA, the White House Council of Economic Advisers has estimated that it means 24,000 deaths per year nationwide are averted because of the ACA. (Others, including researcher Harold Pollack, have made the same calculation.)

Unlike the observational studies, which simply compare the uninsured with those who have insurance, these more recent quasi-experiments tell us what happens when uninsured people gain coverage. This is a much more reliable way to find out how many deaths insurance may have averted. And even though they come to different conclusions, they both suggest we’d see a lot of people die if Obamacare is destroyed.

More people would die if the ACA is repealed than are killed by firearm homicides, HIV, and skin cancer each year

So if we trust these “quasi-experiments,” we’re looking at somewhere between 24,000 and nearly 44,000 extra deaths per year if 20 million people lose health insurance with an Obamacare repeal.

That’s still a sizable range, so I reached out to the author on these last two studies, Benjamin Sommers, to ask him about which he thinks is the better model for estimating the impact of repealing the ACA.

Sommers, a health economist and physician at Harvard University who has extensively researched the effects of health insurance, argued for the Massachusetts figure as the “more cautious and reasonable estimate.” The 2006 health care reform in the state became the model for the ACA, so he thinks the experience there — and the population it affected — is a better match for what’s happened nationally than the Medicaid expansion study in New York, Maine, and Arizona.

And 24,000 is still a large number. That’s more than the death tolls from firearm homicides, HIV, and skin cancer in the US each year.

Again, the Congressional Budget Office analysis suggests 22 million people will lose insurance under the GOP Senate’s Better Care Act, which is more than the 20 million these mortality estimates are based on. The CBO estimates the plan will include particularly steep cuts to Medicaid, which covers the most vulnerable Americans, including pregnant women, the disabled, children, and the working poor. It’s their lives that are on the line now.