Several people contributed to the work described in this paper. J.A.R. and J.E.D. collected data and assessed students’ theses. J.E.D. and T.D., in close collaboration with J.A.R., conducted subsequent data analysis. J.A.R. supervised the research and the development of the manuscript. J.E.D. wrote the first draft of the manuscript; all authors subsequently took part in the revision process and approved the final copy of the manuscript. The research described in this paper was supported in part by the National Science Foundation under award 1225768. The use of human subjects was approved by the Duke University Institutional Review Board.