The Trump administration also reduced advertising for the insurance signup period and made it harder for people to sign up for insurance later in the year, two factors that could have also depressed insurance enrollment. It’s also possible that some who stopped buying their own insurance did so because they got a new job with health care benefits.

But it’s reasonable to think that most of the attrition can be attributed to the spike in prices, as the Trump administration concludes.

The Affordable Care Act of 2010 set up a system where people could buy insurance on online marketplaces. People below the income threshold could qualify for subsidies if insurance in their area became too costly. People above the income threshold could buy insurance in the marketplace, or they could buy a different set of plans directly from an insurance company or through a broker.

The Obama administration frequently published information about enrollment in the official marketplaces, where more than 80 percent of customers qualified for subsidies each year. But researchers had been relying on informal estimates from the insurance industry about enrollment from those who bought coverage directly. The new report provides more official numbers on those who bought insurance themselves. It shows that signups among people who didn’t use a subsidy fell by 1.3 million people between 2016 and 2017, the most recent year with full data.

An earlier government estimate suggested that about 300,000 people who didn’t qualify for help paying their premiums in 2016 would qualify in 2017. If that calculation proved true, enrollment among people without subsidies actually fell by around a million people.