Research scientists Cameron Marlow and D.J. Patil have unprecedented windows into the social interactions of people around the world. Marlow is manager of a data science team for Palo Alto’s Facebook Inc., which has more than 400 million members who come to socialize online. Patil is chief scientist and senior director of product analytics at Mountain View’s LinkedIn Corp., which has more than 65 million members of a social network that concentrates on building professional relationships.

They are at their computers each day, extrapolating information from more than just the tiny “representative samples” traditionally employed by pollsters. These in-house researchers have access to the interactions of groups of people that outnumber populations of whole countries, giving them the kinds of documentable insights into human behavior that generations of researchers before them could only imagine.

During recent interviews with The Chronicle, Marlow and Patil described the trends they are seeing. Facebook, for example, has developed a “Gross National Happiness Index” that measures the positive and negative sentiments expressed in status posts. The application - viewable at apps.facebook .com/gnh_index - can be sorted by country.

Facebook has been criticized for pushing too much personal information into the public view. But Marlow said he and his team of a dozen researchers don’t see anyone’s private information.

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