1. Kathryn H Schmitz, PhD, MPH, FACSM University of Pennsylvania School of Medicine, Division of Clinical Epidemiology, 423 Guardian Drive, 903 Blockley Hall, Philadelphia, PA 19104-6021, USA, Tel.: +1 215 898 6604, Fax: +1 215 573 2265,
2. Rebecca M Speck, MPH University of Pennsylvania School of Medicine, Division of Clinical Epidemiology, 423 Guardian Drive, 1st floor, Philadelphia, PA 19104-6021, USA, Tel.: +1 215 898 0901, Fax: +1 215 573 2265,