Existing data on income and growth in sub-Saharan African countries are unreliable, even seriously misleading. The author provides the first systematic analysis of the level, direction and causes of the errors, looking at a range of African countries, from Benin to Zambia, including South Africa. He then describes why these errors matter. What seem like dry numbers actually have a huge impact on the welfare of these developing countries. Economic growth rate estimates and per-capita income statistics are vital for local governments and for economic aid. Jerven's research suggests that data supplied by national records and statistical offices substantially misstate the actual situation. As a result, scarce economic aid is misapplied, policymakers' attempts to improve their citizens' lives are frustrated, and donors have no accurate sense of the impact of their aid. Jerven explains what can and should be done to improve the guidelines for both the production and use of statistics.