Gary King is the Albert J. Weatherhead III University Professor at Harvard University. His books include A Solution to the Ecological Inference Problem (Princeton). Robert O. Keohane is professor emeritus of international affairs at Princeton University. His books include After Hegemony (Princeton). Sidney Verba (1932-2019) was the Carl H. Pforzheimer University Professor Emeritus and research professor of government at Harvard. His books include Unequal and Unrepresented (Princeton). King, Keohane, and Verba have each been elected as members of the National Academy of Sciences.