Adoption of home broadband has stalled in the United States, as more Americans opt for Internet on the go with mobile devices, a survey showed Monday.

A Pew Research Center survey found 67 percent of Americans had high-speed Internet at home in 2015, down slightly from 70 percent in 2013.

Pew said that this “small, but statistically significant” decline puts broadband back to 2012 levels, and is likely due to the growing number of adults who are “smartphone only” Internet users.

The decline “could represent a blip or might be a more prolonged reality,” the Pew report said.

Some 13 percent of those surveyed said they used smartphones exclusively for Internet in 2015, up from eight percent two years earlier.

Overall, the percentage with Internet access through either a smartphone or a home broadband subscription has changed little since 2013—80 percent this year compared with 78 percent two years earlier.

Pew researchers noted, however, that people dependent on smartphones sometimes face challenges in some online activities, such as applying for jobs.

“Those who are ‘smartphone dependent’ for access encounter distinct challenges,” said researcher John Horrigan.

“If they have both kinds of access, most people prefer to use their smartphone for getting in touch with family or friends but prefer a device that uses a home broadband connection for watching video. At the same time, many ‘smartphone only’ users sometimes struggle to do some of the things they want to do online.”

Many of the “smartphone only” Americans are people with relatively low incomes, African Americans or rural residents.

Those without broadband at home acknowledged they were at a disadvantage in terms of finding a job, getting information about health or government services or keeping up with news.

Among those without home broadband, one-third cited the monthly cost of service as the main reason while 10 percent cited the cost of owning a computer.

Pew found 68 percent in the survey owned a smartphone, a sharp rise from 55 percent two years ago.

The survey also found 15 percent of adults were “cord cutters,” who lack a paid cable or satellite television service.

Many said they are able to get the television they want from online sources like Netflix, Hulu or YouTube.

The report is based on a survey of 2,001 American adults in June and July of 2015, with comparison to research conducted in 2013.

The margin of error for the latest survey was estimated at 2.5 percentage points.