We thank Mihai Codreanu, Anna Dreber Almenberg, Angela Duckworth, Thomas Graeber, Donald Green, Ian Krajbich, David McKenzie, Rachael Meager, Barbara Mellers, Edward Miguel, Katherine Milkman, Don Moore, Brian Nosek, Ricardo Perez-Truglia, Philip Tetlock, Mattie Toma, Severine Toussaert, Robb Willer and audiences at EIEF, FRI, UC Berkeley, UCLA and USC. We are grateful to an outstanding team of research assistants -- Leo Dai, Kevin Didi, Malek Hassouneh, Rohan Jha, and Francis Priestland. We also thank Gary Menezes, Nicholas Otis and Jo Weech for their important roles at the SSPP. We acknowledge gratefully funding from the Alfred P. Sloan Foundation, the Founders' Pledge, Open Philanthropy, and another anonymous foundation. The views expressed herein are those of the authors and do not necessarily reflect the views of the National Bureau of Economic Research.