Depending on how data was collected, it can be classified as declared, inferred or modelled. Declared data is given by the users themselves, and might include things such as age, gender, interests and so on. Facebook is a treasure trove of declared data, from user profiles to things they like or share. Declared data is commonly collected from registration forms, or by running sweepstakes. Inferred data is not given by the users directly, but is deduced – usually from their behavior. Someone reading a lot of computer game reviews is likely to be interested in playing computer games. Finally,
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