David M. Cutler is a professor of economics at Harvard University, a research associate of the National Bureau of Economic Research, and the editor of "The Changing Hospital Industry," published by the University of Chicago Press. Ernst R. Berndt is a professor of applied economics at MIT's Sloan School of Management, director of the NBER's Program on Technological Progress and Productivity Measurement, and coeditor of "Fifty Years of Economic Measurement," published by the University of Chicago Press.