David Lazer, an expert in social net­works and their effects on pol­i­tics and orga­ni­za­tions and one of the 42 tenured and tenure-​​track pro­fes­sors to join North­eastern this fall, has shown how cell phone usage pat­terns can pre­dict friend­ship. Lazer joins the uni­ver­sity from Harvard’s Kennedy School of Gov­ern­ment with a joint appoint­ment in polit­ical sci­ence and com­puter science.

The proof appears in his article on cell phone usage that recently appeared in the Pro­ceed­ings of the National Academy of Sci­ences. The article exam­ines how pat­terns of cell phone use and the prox­imity of one cell phone to the next can demon­strate levels of friend­ship among people. Researchers were able to deduce the degree of a friend­ship by ana­lyzing these patterns—patterns Lazer refers to as “dig­ital breadcrumbs.”

Friend­ship is some­thing that is hard to observe because, in a deep sense, it exists in someone’s head,” he says. “People can be friends with someone they haven’t seen for years or rarely talk with.”

The study, con­ducted with Nathan Eagle of the Santa Fe Insti­tute in New Mexico and col­league Sandy Pent­land of the Mass­a­chu­setts Insti­tute of Tech­nology, doc­u­mented cell phone use pat­terns, or “behav­ioral sig­na­tures,” by tracking the number of calls between phones and how far apart the cell-​​phone users were from one another. The study con­cluded, with 95 per­cent accu­racy, that pat­terns of use and prox­imity could pre­dict which of the study vol­un­teers would iden­tify them­selves as friends.

At North­eastern Lazer plans to use this finding to expand his analysis of data on every­thing from human inter­ac­tions during polit­ical elec­tions to behav­ioral pat­terns during flu season. He also plans to work with Northeastern’s media lab researching tele­phone data to better under­stand the struc­tures of society and who talks with whom.

Lazer will con­tinue to direct Harvard’s Pro­gram on Net­worked Gov­er­nance, which fos­ters research on the inter­con­nect­ed­ness of gov­ern­mental units and pro­vides a forum to dis­cuss the chal­lenges of hier­ar­chical, top-​​down government.

He’ll now also work with Northeastern’s Center for Com­plex Net­work Research, con­sid­ered the world’s leading research center in net­work sci­ence. Lazer has already worked with the Center’s director, Albert-​​László Barabási, a dis­tin­guished physics pro­fessor and leading net­work sci­en­tist. Their coau­thored article, “Com­pu­ta­tional Social Sci­ence,” appeared in the Feb­ruary issue of Science.

The article notes that the capacity to col­lect and ana­lyze tremen­dous amounts of data has trans­formed fields such as physics and biology, but that com­pu­ta­tional social sci­ence fields, such as eco­nomics, soci­ology, and polit­ical sci­ence, have only begun to leverage this capacity “with an unprece­dented breadth, depth, and scale.”

We’re trying to build a bridge between old methods [of data col­lec­tion] and new,” Lazer says. “The social sci­ences need to change in reac­tion to the avail­ability of data.”