The percentage of Americans using the Internet has remained unchanged for the past three years, with older and low-income people making slow progress getting online, a study showed Friday.

The Pew Research Center report showed 84 percent of American adults using the Internet in 2015, the same as in 2013 and 2014 and up just one point from 2012. The number is up sharply, however, from 2000 when just 52 percent were online.

"For some groups, especially young adults, those with high levels of education, and those in more affluent households, Internet penetration is at full saturation levels," the report said.

"For other groups, such as older adults, those with less educational attainment, and those living in lower-income households, adoption has historically been lower but rising steadily, especially in recent years. At the same time, digital gaps still persist."

Among those over 65, the percentage who use the Internet was 58 percent, a modest increase from recent years. But 96 percent of those between 18 and 29 were going online, the survey found.

Internet penetration among those with less than a high school education was 66 percent, a gain of 11 percentage points from 2014. For those with a college degree, 95 percent were online.

Among low-income adults -- those earning less than $30,000 annually -- 74 percent were using the Internet, a number unchanged from a year ago and just three points higher than in 2012. But 97 percent of people with incomes above $75,000 reported being connected.

"These trends have been consistent over time, although the more recent rise of smartphones has provided Internet access to lower-income people, sometimes with lower prices, sometimes with other attractive technology features," the researchers said.

Rural residents were also less likely to be using the Internet -- 78 percent compared with 85 percent of urban and suburban dwellers.

The report analyzed some 97 surveys since 2000 of American adults including two surveys of 3,004 Americans in 2015. The margin of error for the most recent survey was two percentage points.