Global citimpact: 6.64 Researcher at Ifakara Health Institute, Dar es Salaam, Tanzania, National Bureau of Statistics, Dar es Salaam, Tanzania and London School of Hygiene and Tropical Medicine, London, Ifakara Health Institute, Dar es Salaam, Tanzania, National Bureau of Statistics, Dar es Salaam, Tanzania and London School of Hygiene and Tropical Medicine, London, .