This post originally appeared at MotherJones.com.

Facebook users and privacy advocates erupted in anger recently after New Scientist drew attention to a 2012 study in which Facebook researchers had attempted to manipulate users' moods. "The company purposefully messed with people's minds," one privacy group complained to the Federal Trade Commission.

But the mood study is far from the only example of Facebook scrutinizing its users—the company has been doing that for years, examining users' ethnicities, political views, romantic partners, and even how they talk to their children. (Unlike the mood study, the Facebook studies listed below are observational; they don't attempt to change users' behavior.) Although it's unlikely Facebook users have heard about most of these studies, they've consented to them; the social network's Data Use Policy states: "We may use the information we receive about you…for internal operations, including troubleshooting, data analysis, testing, research and service improvement."

Below are five things Facebook researchers have been studying about Facebook users in recent years. (Note that in each of these studies, data was analyzed in aggregate and steps were taken to hide personally identifiable information.)

1. Your significant others (and whether the relationship will last): In October 2013, Facebook published a study in which researchers tried to guess who users were in a relationship with by looking at the users' Facebook friends. For the study, Facebook researchers randomly chose 1.3 million users who had between 50 and 2,000 friends, were older than 20, and described themselves as married, engaged, or in a relationship. To guess whom these users were dating, the researchers analyzed which of the users' friends knew each other—and which ones didn't. You might share a ton of college friends with your old college roommate on Facebook, for example. But your boyfriend might be Facebook friends with your college friends, your coworkers, and your mom—people who definitely don't know each other. Hence, he's special.

Using this method, researchers were able to determine a person's romantic partner with "high accuracy"—they were able to guess married users' spouses 60 percent of the time by just looking at users' friend networks. The researchers also looked at a subset of same-sex couples, to see whether that changed the results. (It didn't.)

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