Facebook users have lower overall grades than non-users, according to a survey of college students who also ironically said the social networking site does not interfere with studying.

That disconnect between perception and reality does not necessarily mean that Facebook leads to less studying and worse grades -- the grades association could be caused by something else. However, it does raise more questions about how students spend their time outside class on activities such as Facebook, part-time jobs and extracurricular activities.

"I'm just saying that there's some kind of relationship there, and there's many third variables that need to be studied," said Aryn Karpinski, an education researcher at Ohio State University.

Her study found that Facebook user GPAs were in the 3.0 to 3.5 range on average, compared to 3.5 to 4.0 for non-users. Facebook users also studied anywhere from one to five hours per week, compared to non-users who studied 11 to 15 or more hours per week.

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