Mr. Messina is understandably proud of his team, which included an unprecedented number of data analysts and social scientists. As a social scientist and a former computer programmer, I enjoy the recognition my kind are getting. But I am nervous about what these powerful tools may mean for the health of our democracy, especially since we know so little about it all…

What I really worry about, though, is that these new methods are more effective in manipulating people. Social scientists increasingly understand that much of our decision making is irrational and emotional. For example, the Obama campaign used pictures of the president’s family at every opportunity. This was no accident. The campaign field-tested this as early as 2007 through a rigorous randomized experiment, the kind used in clinical trials for medical drugs, and settled on the winning combination of image, message and button placement. I agree that his family is wonderful and his daughters are cute. But an increasing role of “likability” factors, which we now understand better how to manipulate, is not good for democracy…

I’m not claiming that the Obama campaign used these methods to mislead. However, the fact that the winning campaign’s “chief data scientist” was previously employed to “maximize the efficiency of supermarket sales promotions” does not thrill me. You should be worried even if your candidate is — for the moment — better at these methods. Democracy should not just be about how to persuade people to vote for one candidate over another by any means necessary.