The percentage of Texans without health insurance dropped 31 percent since enrollment began in the Affordable Care Act's (ACA) Health Insurance Marketplace, according to a new report released by the Episcopal Health Foundation and Rice University's Baker Institute for Public Policy.

The report found that from September 2013 to March 2015, the percentage of uninsured adult Texans ages 18-64 dropped from 25 to 17 percent.

"This is a dramatic drop that's unprecedented in Texas," said Elena Marks, president and CEO of the Episcopal Health Foundation and a health policy scholar at the Baker Institute. "It's almost entirely attributable to newly insured individuals who purchased their own health insurance plans. The drop in the uninsured rate occurred across all income levels and age groups, including younger adults."

Despite this improvement, Texas remains the state with the highest percentage of people without health insurance, and for the first time, Texas now has the largest number of uninsured residents in the country.

The report found that the poorest Texans had the lowest drop in the uninsured rate. While there was a 45 percent drop in the uninsured rate for individuals earning more than $16,000 a year, the decrease was only 20 percent for those with lower incomes.

"The lowest-income Texans are almost four times more likely to be uninsured than those with higher incomes," said Vivian Ho, the chair in health economics at Rice's Baker Institute, a professor of economics at Rice and a professor of medicine at Baylor College of Medicine. "This coverage gap has grown since 2013 primarily because the ACA Marketplace allows households above the federal poverty level to buy health insurance using subsidies. Those same levels of discounts are not available to Texans with incomes below the federal poverty level."

Individuals who earn below $16,000 are able to enroll in Medicaid in the 31 states that opted to expand Medicaid. In Texas, those same individuals are not eligible for Medicaid coverage because state leaders chose not to accept federal funding for Medicaid expansion.

"Unless Texas participates in an expanded Medicaid program or develops some other mechanism for covering the lowest-income Texans, the number who remain uninsured is not likely to change," Ho said. "Right now, those at the lowest incomes must rely on health care that is highly subsidized by county and state tax dollars, or get by without needed health care."

The 31 percent decrease in the rate of uninsured Texans was similar to drops in other states that did not expand Medicaid coverage, but much lower than the 53 percent average decrease in states that did expand Medicaid coverage, the report found.

The report is the 11th in a series on the implementation of the ACA in Texas co-authored by Marks and Ho.

The Health Reform Monitoring Survey (HRMS) is a quarterly survey of adults ages 18-64 that began in 2013. Today's report is a summary of data extracted from the HRMS Surveys in Texas administered between September 2013 and March 2015.