[1] South African Med Res Council, Biostat Res Unit, ZA-4001 Durban, South Africa
[2] Univ KwaZulu Natal, Sch Math Stat & Comp Sci, ZA-3201 Pietermaritzburg, South Africa
[3] South African Med Res Council, Biostat Res Unit, ZA-0001 Pretoria, South Africa
[4] Univ Pretoria, Dept Stat, ZA-0001 Pretoria, South Africa
[5] South African Med Res Council, SAFOODS Div, Biostat Res Unit, ZA-8001 Cape Town, South Africa
[6] Stellenbosch Univ, Dept Global Hlth, Div Human Nutr, ZA-8001 Cape Town, South Africa