[1] Department of Clinical Epidemiology, Canadian Coll. of Naturopathic Med., North York, Ont.
[2] Dept. of Clin. Epidemiol./Biostatist, McMaster University, Hamilton, Ont. L8N 3Z5
[3] London Sch. of Hygiene/Tropical Med., University of London, London
[4] Institute of Medical Sciences, University of Toronto, Toronto, Ont.
[5] Department of Internal Medicine, Mayo Clinic College of Medicine, Rochester, MN