During the first quarter of 2015, the uninsured rate for adults in the U.S. was the lowest since Gallup and Healthways began tracking the data in 2008.

The uninsured rate was 11.9 percent in the first quarter, down from 12.9 percent in the fourth quarter of 2014 and from a high of 18.0 percent in the third quarter of 2013.

The decline coincides with the Patient Protection and Affordable Care Act’s individual mandate, which went into effect last year. According to the provision, most people are required to have insurance or pay a tax as a penalty.

The survey included responses from 43,575 adults from Jan. 2 to March 31, 2015. Each day, Gallup and Healthways asked 500 adults via telephone if they had insurance. The adults were from all 50 states and the District of Columbia.

For families with an annual household income below $36,000, the uninsured rate decreased 8.7 percentage points from the end of 2013 to the first quarter of 2015. During that same time period, the uninsured rate among Hispanics decreased 8.3 percentage points. The rate for people from 26 to 34 years of age decreased 7.4 percentage points and the rate for blacks decreased 7.3 percentage points.

The survey’s authors mentioned the uninsured rate could decrease again in the second quarter because President Obama’s administration created a special enrollment period from March 15 through April 30 for people to purchase coverage. A few states that run their own exchanges have also allowed people to sign up for health insurance through April 15, when taxes are due.