1 Division of Preventive and Behavioral Medicine, Department of Population and Quantitative Health Sciences, University of Massachusetts Medical School, Worcester, Massachusetts, U.S.A.
2 Physical Activity Policy Research and Evaluation Network.
3 Division of Nutrition, Physical Activity and Obesity, Centers for Disease Control and Prevention, Atlanta, Georgia, U.S.A.
4 Division of Health Policy and Administration, School of Public Health, University of Illinois Chicago, Chicago, Illinois, U.S.A.