Facebook (and Youtube and Twitter) have conducted a global experiment on human populations without consent of the guinea pigs by analyzing our “Likes”.
Facebook’s digital model of us is more accurate than our own understanding of ourselves.
Computers need evaluate as few as 100 Likes to make a judgement more effective than a human. Analyzing just 300 Likes enables the model to know more about the subject than does the subject’s spouse. Computer models achieve “peak” accuracy when more than 500 Likes are observed.

We show that (i) computer predictions based on a generic digital footprint (Facebook Likes) are more accurate (r = 0.56) than those made by the participants’ Facebook friends using a personality questionnaire (r = 0.49); (ii) computer models show higher interjudge agreement; and (iii) computer personality judgments have higher external validity when predicting life outcomes such as substance use, political attitudes, and physical health; for some outcomes, they even outperform the self-rated personality scores. Computers outpacing humans in personality judgment presents significant opportunities and challenges in the areas of psychological assessment, marketing, and privacy.
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Given the variety of objects, subjects, brands, and people that can be liked and the number of Facebook users (>1.3 billion), Likes represent one of the most generic kinds of digital footprint. For instance, liking a brand or a product offers a proxy for consumer preferences and purchasing behavior; music-related Likes reveal music taste; and liked websites allow for approximating web browsing behavior. Consequently, Like-based models offer a good proxy of what could be achieved based on a wide range of other digital footprints such as web browsing logs, web search queries, or purchase records

Reference
Youyou, W., Kosinski, M., Stillwell, D. (2015). “Computer-based personality judgements are more accurate than those made by humans”. PNAS. January 27, 2015. https://doi.org/10.1073/pnas.1418680112 Retrieved from: http://www.pnas.org/content/112/4/1036 on April 3, 2018.
Likes are the Secret Sauce of Social Media Surveillance
“Likes” are the secret sauce. We give Likes out of kindness and believing we may have been thoughtful towards a “Friend”. We give Likes, sometimes as a form of “bookmark” so we can find something later, by reviewing our Likes. The entire process was conceived as a form of mind control, to cause us to reveal our thought processes and patterns.
We now know – never, ever click Like on Facebook or Youtube or Twitter and never click +1 on Google platforms. It is unclear what is collected by Instagram and how Likes are evaluated on that platform but it is presumed that Instagram (aka Facebook) ties photo Likes to the image tags used in photo descriptions.
These platforms have created a psychological profile of every user. The analysis includes not only our Likes, but our Group memberships, our self selected Interests (Page Likes, especially), our self provided background such as education or religious interests, an analysis of our text, analysis of our online web site visits (Facebook and Google both track our web site visits across the web), and may include text analysis of posts we have made on other web sites or web sites that we operate ourselves, such as blogs like this one.
While Facebook let’s us download “our data”, Facebook does not provide us with the psychological model they have created about each of us. We do not know what it contains nor do we have any way to correct errors in that model.