1. Epidemiology and Public Health, Institute of Biomedical and Clinical Science, University of Exeter Medical School, Exeter, United Kingdom
2. Health Statistics Research Group, Institute of Health Research, University of Exeter Medical School, St Luke’s Campus, Exeter, United Kingdom
3. University of Connecticut Center on Aging, University of Connecticut Health, Farmington
4. Longitudinal Studies Section, National Institutes of Health, Harbor Hospital, Baltimore, Maryland