for their children's education. Most of the emerging middle class consists of people who are middle class by the standards of the developing world but not the developed one, since their money incomes do not match developed country levels, but the percentage of it which is discretionary does. By this definition, the number of middle-class people in Asia exceeded that in the West sometime around 2007 or 2008. The Economist article pointed out that in many emerging countries, the middle class has not grown incrementally but explosively. The point at which the poor start entering the middle class by the millions is alleged to be the time when poor countries get the maximum benefit from cheap labour through international trade, before they price themselves out of world markets for cheap goods. It is also a period of rapid urbanization, when subsistence farmers abandon marginal farms to work in factories, resulting in a several-fold increase in their economic productivity before their wages catch up to international levels. That stage was reached in China some time between 1990 and 2005, when the Chinese "middle class" grew from 15% to 62% of the population and is just being reached in India now. The Economist predicted that surge across the poverty line should continue for a couple of decades and the global middle class will grow exponentially between now and 2030. Based on the rapid growth, scholars expect the global middle class to be the driving force for sustainable development. This assumption, however, is contested (see below). As the American middle class is estimated by some researchers to comprise approximately 45% of the population, The Economist article would put the size of the American middle class below the world average. This difference is due to the extreme difference in definitions between The Economist and many other models. In 2010, a working paper by the OECD asserted that 1.8 billion people were now members of the global "middle class". Credit Suisse's Global Wealth Report 2014, released in October 2014, estimated that one billion adults belonged to the "middle class," with wealth anywhere between the range of $10,000–$100,000. According to a study carried out by the Pew Research Center, a combined 16% of the world's population in 2011 were "upper-middle income" and "upper income". An April 2019 OECD report said that the millennial generation is being pushed out of the middle class throughout the Western world.