A survey showing 21 percent of Americans are online “almost constantly” is undermined by a lack of clear definition. Indeed, the more surprising stat may be the 13 percent who say they don’t use the Internet at all.

The figures come from the Pew Research Center, which regularly runs surveys on tech and Internet use. For the most part Pew’s surveys tend to be rigorous and credible, so it’s a surprise that it’s used some vague wording.

The headline question in the survey, conducted among adults, was how often they go online. The responses were:

• 21 percent “Almost constantly”;
• 42 percent “Several times a day”;
• 10 percent “About once a day”;
• 6 percent “Several time a week”;
• 7 percent “Less often”; and
• 13 percent said they don’t use the Internet.

The demographic breakdown is much as you’d expect. There’s no significant gender or race differences, but being younger, better educated and richer all make you more likely to be online “almost constantly”, which could be a combination of more disposable income for gadgets, being more tech-savvy, and working in Internet-dependent jobs.

Though Pew has tackled the topic before, it’s the first time it’s added the “Almost constantly” category. The problem is the 21 percent figure makes for an eyegrabbing headline claim, it’s unclear exactly what that entails for the people in that category.

At one extreme it could be the stereotypical example of a technozombie who barely takes their eyes off the screen during their waking hours. At the other, it could simply be people who check their email on a phone or computer once an hour or so and use a strict interpretation to categorize that as being more than “several times a day.”

There’s also the problem of treating all “online” activity the same. For example, picture somebody who listens to music during a train ride home, watches a movie, then plays a video game before bed. If they are listening to an album on their iPod, watching a TV network, then playing a single-player game, that could be classed as zero hours “online.”

However, if they stream music from Spotify, watch a Netflix title, then play multiplayer, they’ve been carrying out exactly the same activities but could technically class themselves as having spent four hours online.

The Verge notes Pew has had problems in the past with asking respondents to assess the time they spent using tech. In one survey, 14 percent of people said they use their phone browser “continuously” which seems unlikely to say the least.