Three approaches to GDP and why two fail in Africa

The system of national accounts requires deriving GDP three independent ways: the expenditure approach (the Keynesian C+I+G+net exports, but consumption is unknown without reliable household surveys so it is always derived as a residual), the income approach (wages+profits+rents, uncomputable because most operators have no formal wage and barter), and the production approach (summing industrial sectors from agriculture down to government and NGOs); in sub-Saharan African statistical offices only the production approach is actually used.