1. Department of Medicine, Tufts Medical Center, Boston, Massachusetts, USA.
2. Tufts University School of Medicine, Boston, Massachusetts, USA.
3. Greater Lawrence Family Health Center, Lawrence, Massachusetts, USA.
4. Department of Family Medicine, Tufts University School of Medicine, Boston, Massachusetts, USA.
5. Department of Pediatrics, University of Massachusetts Medical Center, Worcester, Massachusetts, USA.
6. Department of Biostatistics, School of Public Health, Boston University, Boston, Massachusetts, USA.