This includes 12 countries for which Greenberg's diversity index exceeds 0.9, meaning that a pair of randomly selected people will have less than 10% chance of having the same mother tongue. However, the primary language of government, political debate, academic discourse, and administration is often the language of the former colonial powers; English, French, or Portuguese. Trade-based theories Dependency theory asserts that the wealth and prosperity of the superpowers and their allies in Europe, North America and East Asia is dependent upon the poverty of the rest of the world, including Africa. Economists who subscribe to this theory believe that poorer regions must break their trading ties with the developed world in order to prosper. Less radical theories suggest that economic protectionism in developed countries hampers Africa's growth. When developing countries have harvested agricultural produce at low cost, they generally do not export as much as would be expected. Abundant farm subsidies and high import tariffs in the developed world, most notably those set by Japan, the European Union's Common Agricultural Policy, and the United States Department of Agriculture, are thought to be the cause. Although these subsidies and tariffs have been gradually reduced, they remain high. Local conditions also affect exports; state over-regulation in several African nations can prevent their own exports from becoming competitive. Research in Public Choice economics such as that of Jane Shaw suggest that protectionism operates in tandem with heavy State intervention combining to depress economic development. Farmers subject to import and export restrictions cater to localized markets, exposing them to higher market volatility and fewer opportunities. When subject to uncertain market conditions, farmers press for governmental intervention to suppress competition in their markets, resulting in competition being driven out of the market. As competition is driven out of the market, farmers innovate less and grow less food further undermining economic performance. Governance Although Africa and Asia had similar levels of income in the 1960s, Asia has since outpaced Africa, with the exception of a few extremely poor and war-torn countries like Afghanistan and Yemen. One school of economists argues that Asia's superior economic development lies in local investment. Corruption in Africa consists primarily of extracting economic rent and moving the resulting financial capital overseas instead of investing at home; the stereotype of African dictators with Swiss bank accounts is often accurate. University of Massachusetts Amherst researchers estimate that from 1970 to 1996, capital flight