1. Health Statistics and Geography Lab, Division of Preventive and Behavioral Medicine, University of Massachusetts Medical School, 55 Lake Avenue North, Worcester, MA 01655, USA
2. College of Nursing and Health Sciences, University of Massachusetts Boston, 100 Morrissey Boulevard, Boston, MA 02125-3393, USA
3. Institute for Aging Research, Hebrew SeniorLife/Harvard Medical School and Beth Israel Deaconess Medical Center, 1200 Centre Street, Boston, MA 02131-1097, USA