1. Department of Health Care Policy, Harvard Medical School, and Department of Biostatistics, Harvard T.H. Chan School of Public Health, Boston, Massachusetts 02115;
2. Department of Quantitative Health Sciences, University of Massachusetts Medical School, Worcester, Massachusetts 01605;
3. Department of Statistics, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213;
4. Institute for Clinical Evaluative Sciences, Toronto, Ontario M4N 3M5, Canada, and the Institute of Health Policy, Management & Evaluation, University of Toronto, Toronto, Ontario M5T 3M6, Canada, and Dartmouth Institute for Health Policy and Clinical Practice, Hanover, New Hampshire 03766;
5. Department of Statistics, University of California, Irvine, California 92697;
6. Department of Biostatistics, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland 21205;