yahoo ceo marissa mayer at davos
World Economic Forum
Last week, Yahoo banned employees from working from home.

How did CEO Marissa Mayer decide to make such a controversial decision?

According to a source, the only way Mayer is comfortable making any decision: with the help of data.

Like a lot of companies, Yahoo has something called a Virtual Private Network or VPN. Remote workers can use it to securely log into Yahoo's network and do work.

(LifeHacker has a really good explanation of what a VPN is.)

After spending months frustrated at how empty Yahoo parking lots were, Mayer consulted Yahoo's VPN logs to see if remote employees were checking in enough.

Mayer discovered they were not — and her decision was made.

Kara Swisher first reported the news that Mayer was showing executives Yahoo's VPN logs to justify her work-from-home ban.

Mayer is famously obsessed with metrics and data.

Once, a Google designer quit the company in a huff because he was tired of how Mayer, in charge of how homepage looked, would choose design elements like color or font not based on taste, but raw data.

For every design variable, she looked at how users interacted with Google with one design — and then the other.

If the data showed users were using faster one way instead of the other, that particular design choice won out.

It's hard to argue that Mayer's process didn't work for Google. It was not the first search engine on the market, but it's just about the only one anybody uses now.

Likewise, we're hearing from people close to Yahoo executives and employees that she made the right decision banning work from home.

"The employees at Yahoo are thrilled," says one source close to the company.

"There isn't massive uprising. The truth is, they've all been pissed off that people haven't been working."

Now Watch: Here's How You Can Boost Your Productivity At The Office