Keeping parts of your life secret from strangers online is usually a good idea. But could even your closest friends know things about you that you'd never tell anyone?
A recent study in Proceedings of the National Academy of Sciences shows that there is a lot you can discover about a person based on what pages they "like" on Facebook.
Between 2007 and 2012, researchers at Cambridge University collected data from over 58,000 U.S. Facebook users, including profile information and results of personality tests, and created a model to mount predictions.
Users can keep up with news about musicians, politicians, causes, sports teams, TV shows, and websites like PolicyMic by liking the entity's Facebook page. There are also more absurd pages like "The lamp that ghetto stomps the 'i' in Pixar" and "The Norwegian Olympic Curling Team's Pants."
One of the study's authors, David Stillwell, said the results might come as a surprise.
"Your likes may be saying more about you than you realize," he said.
It turns out that researchers were able to correctly deduce qualities like a user's gender, race, age, religion, sexuality, substance use and political views. The likes could also predict relationship status, number of Facebook friends, as well as half a dozen different personality traits.
According to the study, a person's likes can also be used to predict intelligence. Pages that correlated to this include The Daily Show, "science," "Morgan Freeman's Voice" and, strangely, "Curly Fries." Lower intelligence was correlated to liking "Clark Griswold," "Harley-Davidson" and "Bret Michaels."
But more than this, a person's likes can predict even more personal aspects of their lives that could affect their personality.
Interestingly, users over 21 who liked statements such as "Never Apologize For What You Feel It's Like Saying Sorry For Being Real" or "I'm The Type Of Girl Who Can Be So Hurt But Still Look At You & Smile" were slightly more likely to have divorced parents.
"Facebook likes have a meaning that we can use to understand the psychology behind what people do," said Stillwell. "[They give] us a poignant insight into the effects that parental breakup has on children even after they grow up."
Rebecca Lieb, a digital media analyst at the Altimeter Group, a consulting firm in New York City, was unsurprised by the results.
"Advertising and marketing focus on this, but it's important not to isolate this as only an online issue or a social network issue," she said. "Data is being collected at every stage of our lives. If you're using a credit card, you're opening yourself up to as much data collection as if you're using Facebook or searching online and getting cookies collected in your browser."
Similar statistical techniques were used last year, when a story broke about Target learning about a teenager's pregnancy before her father. The girl had been receiving advertisements in the mail for baby clothes and cribs, and after her father angrily stormed into a Target store demanding an explanation, he learned she was due in just a few months.
While Facebook likes can be used in a more favorable manner, by suggesting new restaurants and TV shows based on the information a person has provided, researchers agree that the findings may have "negative implications for personal privacy."
Facebook has already been the target of several complaints regarding a lack of privacy on the website, especially collecting data without users' knowledge. Although users can make certain aspects of your profile private, others are out of their control.
Stillwell's biggest piece of advice for Facebookers whose pages are public is to be careful what you like.
"My biggest concern is that people do not realize what is possible," he said, "so they think that frivolous behaviors such as liking something cannot possibly say anything important about them."