626 Bulletin of the World Health Organization | August 2004, 82 (8)

Reproduced by permission of the International Journal of Epidemiology

627Bulletin of the World Health Organization | August 2004, 82 (8)

628 Bulletin of the World Health Organization | August 2004, 82 (8)

629Bulletin of the World Health Organization | August 2004, 82 (8)

630 Bulletin of the World Health Organization | August 2004, 82 (8)