The challenges of calculating GDP are particularly acute in Sub-Saharan Africa, owing to weak national statistics offices and historical biases that muddy crucial measurements. Bothered by what he regarded as problems in Zambia's national statistics, Morten Jerven, an assistant professor at Simon Fraser University, spent four years examining how African countries obtain their data and the challenges they face in turning them into GDP estimates. His new book, Poor Numbers: How We Are Misled by African Development Statistics and What to Do about It, makes a strong case that many GDP measurements we thought were accurate are not.

Jerven notes that many African countries have trouble measuring the size of their relatively large subsistence economies and unrecorded economic activity. How do you account for the production of a farmer who grows and eats his own food? If subsistence farming is systematically underestimated, some of what looks like growth as an economy moves out of subsistence may merely reflect a shift to something that is easier to capture statistically. Read More