1. Northern Research Station, US Department of Agriculture (USDA) Forest Service, Philadelphia, Pennsylvania 19103, USA;
2. Department of Biostatistics and Epidemiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6021, USA
3. Department of Emergency Medicine, Center for Emergency Care Policy Research, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
4. Department of Criminology, School of Arts and Sciences, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6286, USA
5. Department of Epidemiology, Mailman School of Public Health, Columbia University, New York, NY 10032, USA