A greater percentage of Americans have health insurance than any time in the past 40 years, according to an announcement made by the Obama administration Monday.

Since the major provisions of the Affordable Care Act (ACA) have taken effect, the percent of adults without health insurance has fallen from 20.3 percent to 13.2 percent. An estimated 16.4 million uninsured people have gained health insurance, according to a Department of Health and Human Services (HHS) report.

The report is an analysis of Gallup-Healthways Well-Being Index survey data.

“The Affordable Care Act is working to drive down the number of uninsured and the uninsured rate. Nothing since the implementation of Medicare and Medicaid has seen this kind of change,” said HHS assistant secretary for planning and evaluation Richard Frank, reported Kaiser Health News.

Critics of the ACA dispute the accuracy of the HHS report.

Edmund Haislmaier, senior research fellow for health policy at the Heritage Foundation, a right-wing think-tank, told USA Today that using insurer data is more accurate. Haislmaier says that data shows a net growth of 5.8 million people in the individual insurance market that is offset by a 4.9 million-person decrease in the employer-insured market.

Richard Frank, HHS assistant secretary for planning and evaluation, told USA Today that he disagreed with Haislmaier’s claim.

“We have not seen a drop in employer-based coverage,” Frank said.

Republican opponents of President Obama’s health-care reform law criticized the administration for “celebrating” the HHS report. “Millions of people have lost coverage they liked, and out-of-pocket costs continue to rise. Coverage does not equal care,” said Sen. John Barrasso (R-Wyoming), reported the New York Times.

A report by the Urban Institute disputes Barrasso’s claim. The report found that as few as 400,000 people had individual policies cancelled and just 0.3 percent of Americans lost health insurance through their employer due to the ACA.

Barrasso has long been critical of the ACA, even if those critiques are sometimes not consistent. He has contradicted his previous statements on whether federal subsidies were supposed be delivered through a federal health-care exchange or through state exchanges.

Among the other findings of the HHS report: The ACA has reduced the percentage of people of color and low-income people without health insurance. According to the report, the uninsured rate for Latino people fell from 41.8 percent to 29.5 percent; the uninsured rate for Black people fell from 22.4 percent to 13.2 percent.

The largest reductions in the percentage of low-income people without health insurance were seen in states that expanded Medicaid under the ACA.

States that expanded Medicaid saw the number of low-income people without health insurance decrease by an average of 13 percent, while states that have not expanded Medicaid saw the percentage of low-income people without health insurance decrease by an average of 7 percent.

Several studies and reports have documented the consequences for states—most of them with GOP-controlled legislatures—that have chosen not to expand Medicaid. Under the ACA, the federal government covers the full cost of the expansion for the first three years, and 90 percent of the cost in subsequent years.

To date, 29 states have implemented Medicaid expansion through the ACA, which Gallup recently cited as a major factor in declining uninsured rates.