Facebook announced yesterday that “every post and comment — both public and private — by a U.S. user that mentions a presidential candidate’s name will be fed through a sentiment analysis tool that spits out anonymized measures of the general U.S. Facebook population.” This analysis, along with reader polls and other information, will in turn be shared with politico.com.

The brief announcement of this new feature raises serious questions and offers few answers. Most troubling is Facebook’s willingness to search and collect users’ private political preferences and thoughts, preferences they may have shared only with their closest friend in a private email.

This raises at least three concerns. The first is that many users may not want to be part of any “sentiment analysis” or poll. For example, they may be a firm supporter of Mitt Romney but find Ron Paul’s ideas interesting. Are they now going to feel hesitant to talk about Paul’s ideas out of awareness that it might be registered as support or boost a candidate they don’t like? Second, we don’t see any mention of user consent anywhere in Facebook’s announcement. How has Facebook decided that users agreed that their personal communications can and should be used in this way?

Finally, what other uses might this information be put to in the future? Will it be used to serve users ads from politicians or manipulate voting preferences in some way? We can see the marketing materials from Facebook now: “Candidates, serve ads to secret supporters! No one knows about their preferences except their closest friends and us.”

Worse, what if this secret knowledge is used to shape messages? Users would likely not expect they are getting a Romney ad that highlights libertarianism because in the past they said something positive about Ron Paul in an email.

We place a premium on political speech in the United States and debating candidates’ positions and merits. Because Facebook has become one of the central forums for political debate it has a duty to clearly disclose any practices that threaten to distort that discussion. It can begin by bringing transparency to this process and answering some basic questions – beginning with how it justifies including users’ private communications.

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