WASHINGTON — New surveys provide a glimpse into how many Americans have gained health insurance since the federal and state marketplaces opened in October.

Gallup reported Wednesday that the 21 states and the District of Columbia that fully embraced the new health-care law by setting up their own exchanges and expanding their Medicaid programs saw their uninsured rate drop this year three times faster than the states that did not: a decline of 2.5 percentage points compared with a 0.8-point drop in the 29 other states.

Last week, Gallup said the uninsured rate had fallen from 17.1 percent to 15.6 percent between the fourth quarter of 2013 and the first quarter of 2014 – the lowest rate since 2008.

Another Gallup poll, also released Wednesday, found that 4 percent of Americans said that they are newly insured this year, with slightly more than half(2.1 percent) reporting that they received coverage through an exchange. The rest said they received coverage from another source, which could be either Medicaid, an employer or a health plan purchased directly from an insurer. An additional 7.5 percent said they had a new health plan that replaced an old one.

The poll also found that newly insured people are, on average, younger than the rest of the population. People ages 18 to 29 accounted for 30 percent of the newly insured, although they represent just 21 percent of the population. However, the newly insured in this age bracket were much more likely to get coverage off the exchange (24 percent exchange vs. 37 percent off-exchange).

Gallup found that the newly insured also tend to be lower-income and are more likely to get coverage through the exchanges, in which people earning up to 400 percent of the federal poverty level can receive subsidies to help purchase insurance. The Department of Health and Human Services has previously said that 83 percent of those purchasing through the exchanges received financial assistance.

On Tuesday, the Urban Institute offered further details on its finding that the number of uninsured non-elderly adults fell by 5.4 million people between September and early March. The institute said states that expanded their Medicaid programs saw their uninsured rate drop 4 percent, while states that didn’t expand had a much slower drop of 1.5 percent. The expansion states also did a better job of covering young adults and Hispanics in particular – demographics targeted by supporters of the health-care law.

More surveys are expected on how the Affordable Care Act is changing the uninsured rate. One will come from the Census Bureau, which was the source of some controversy Tuesday after The New York Times reported that an overhaul of the agency’s survey methodology would make it difficult to determine the law’s effect on the uninsured rate. The report raised some eyebrows on the right and left, but the Census Bureau said it will be able to measure the ACA’s impact.

The Census Bureau said late Tuesday that the new survey methodology, first announced in September 2013, will go into effect for data covering the 2013 calendar year. So, while it will be difficult to compare changes in the 2012 and 2013 uninsured rate, it should be possible to make a direct comparison between 2013 and 2014, the start of the law’s coverage expansion.