The number of deaths in the first year of life per 1 000 children born. Poor sanitation is a major factor: this is the ‘urban penalty’/‘urban graveyard effect’ (Mercier and Boone (2002) Hist. Geog. 28, 4). Gyimah (2006) Ethnic. & Health 11, 2 finds that mortality is more of a reflection of socio-economic inequalities than ethnic-specific socio-cultural practices, but notes that wider birth spacing and longer breastfeeding also reduce infant mortality. T. Boley (1999) sees infant mortality as an index of social tension and cultural values.