Customer satisfaction with federally provided services climbed to its highest peak in four years, a survey suggests.

Satisfaction with the federal government had reached an all-time low in 2015, after dipping each year from its all-time high in 2012, according to the American Citizen Satisfaction Index, an economic indicator registered to the University of Michigan.

The improved quality of some federal websites—described as "ease and usefulness"—could explain the sudden surge in satisfaction, the report said. Other driving factors could have been improved "timeliness and efficiency of processes," courtesy and professionalism of federal employees, and the clarity of information that federal agencies disperse.

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On a scale of zero to 100, citizens rated their overall satisfaction with federal services in 2016 at 68, up from 63 in 2015. Among individual agencies, the Interior and State departments led the group with satisfaction scores of 78. Interior users were generally looking up national parks online, and State customers generally referred to their experiences renewing or receiving passports.

The Treasury Department bottomed out the ranking with a score of 59—"not surprising given that its primary citizen-facing agency is the Internal Revenue Service," the report said. The Veterans Affairs Department was second lowest at 66.

ACSI researchers suggested customers' interaction with the Health and Human Services Department may also have driven up satisfaction scores, in addition to better federal websites. Customers of HHS made up a larger percentage of the 2,380 people polled this year versus previous years, and satisfaction with that department jumped 8 percent to 67, potentially because of improvements in HealthCare.gov.

"As the impending fight to scrap and/or replace the [Affordable Care Act] legislation advances in 2017, it will be important to track potential effects on citizen satisfaction," the report said.