Here’s a brief excerpt from an article by Jim Clifton, Chairman and CEO of the Gallup Organization. It is featured by LinkedIn Pulse. To check out all the articles posted by the website’s Influentials, please click here.

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I just read this sentence in a New York Times article on telecommuting: “We know that those who work at home tend to put in longer hours and are often more productive.”

What? Is that the writer’s scientific conclusion? To me, it looks more like a note someone sends to his boss on why he isn’t coming in again today.

A lot of what I read about telecommuting assumes that it’s a good thing and that businesses should allow for more of it. The Times piece cites a survey by the Society for Human Resource Management that “found a greater increase in the number of companies planning to offer telecommuting in 2014 than those offering just about any other new benefit.”

We all hear lots of great anecdotes about productive people working at home in their pajamas or increasing their company’s performance over a latte at the local Starbucks. What’s missing here are data. So I asked Gallup’s best workplace scientists what they could find on telecommuting in our U.S. employee engagement database, which is the largest of its kind. The resulting discoveries offer a mixed picture at best.

On the plus side, people who work remotely less than 20% of the time are the most likely to be engaged of all employees: 35% of those employees are engaged, compared with an average 30% engagement in the overall U.S. workforce.

But active disengagement rises as employees spend more time off-site. Among people who work remotely 20% to 50% of the time, 18% are actively disengaged. That number increases to 22% actively disengaged for employees who work remotely 51% to 99% of the time. And here’s a killer finding: People who spend all of their time working remotely are nearly twice as likely to be actively disengaged (23%) compared with those who telecommute less than 20% of the time (12% actively disengaged).

Pretty simple math here: Working remotely less than 20% of the time is very good for engagement, but doing so 100% of the time is very bad. That’s because actively disengaged employees aren’t just miserable, but they spread their misery among their colleagues. Remote employees may infect their colleagues via email and phone calls, rather than by roaming the halls, but don’t kid yourself: They’re still doing damage to your company.

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Here’s a direct link to the complete article.

Jim Clifton is Chairman and CEO of Gallup. He is author of The Coming Jobs War (Gallup Press, 2011).