There has been a lot of discussion about the viability of GDP as a measure of development (see The Genuine Progress Indicator, an alternative to GDP (Ron Colman)). Here, Morten Jerven discusses another issue with GDP, namely its unreliability (with a focus on Africa). Estimates of economic growth rates and per-capita income are basic to the operation of governments in developing countries and to nongovernmental organizations and other entities that provide financial aid. As Jerven notes, the current catchphrase in the development community is “evidence-based policy,” and scholars are applying increasingly sophisticated econometric methods—but no statistical techniques can substitute for partial and unreliable data. Similar arguments have been put forward regarding extreme poverty calculations (see What is happening to poverty? (Rammelt and Surace)).