Friends Don’t Let Friends Free Ride

* We are grateful to Seth Bromberger and to contributors to open source projects like Julia, LightGraphs, iGraph, and Python. For comments, we thank Guy Grossman, Yue Hou, Horacio Larreguy, Jenn Larson, Michele Margolis, John Marshall, Cyrus Samii, Zachary Steinert-Threlkeld, Dawn Teele, Stephanie Zonszein, Liz Zechmeister, and participants at the NYU Methods Workshop and NEWEPS. We also thank Vanderbilt University for generous access to server time. Disclosure: This work was made possible by a data-sharing agreement between the authors and a telecommunications firm. In exchange for access to the data, the authors provided training in coding and data analysis. At no time did the authors provide the company with any financial compensation, nor did the company provide the authors with any financial compensation.