The study tries to quantify the effect in several ways. One of the sharpest, I think, compares two otherwise similar children in lower-income households — one who grows up in a community where social contacts mostly come from the lower half of the socioeconomic distribution, and another who grows up in a community where social contacts mostly come from the upper half.
The average difference between the two, in terms of their expected adult outcomes, is significant, the authors report. It’s the same as the gap between a child who grows up in a family that makes $27,000 a year and one who grows up in a family that makes $47,000.
The study is based on a dizzying amount of data, including the Facebook friendships of 72 million people. (You can explore the findings through these charts and maps from The Upshot.)
Robert Putnam — a political scientist who has long studied social interactions, including in his book “Bowling Alone” — said the study was important partly because it hinted at ways to increase upward mobility. “It provides a number of avenues or clues by which we might begin to move this country in a better direction,” he said.