More than half the world's population is for the first time living in households earning enough to be considered middle or upper class, with five people joining their ranks every second. The rapid growth of the middle class, most of which is taking place in Asia, will have significant economic and political effects, as people become more demanding of businesses and governments, said Kristofer Hamel, chief operating officer of World Data Lab, the non-profit organisation that compiled the figures. The milestone is important because the middle class is the engine of modern economies," Mr Hamel said, adding that about half of global economic demand is generated by household consumption, with half of this coming from the middle class. The World Data Lab defines middle class as someone earning between $11 and $110 per day, on a 2011 purchasing power parity basis, a benchmark used by many organisations and governments, including India and Mexico. It concluded earlier this month that 3.59bn people make up the global middle class, and forecast that the group would grow to 5.3bn by 2030. Almost 90 per cent of the new middle class is expected to be found in Asia. By 2030, the spending power of the American middle class will remain the greatest in the world - at about $16tn on a 2011 PPP basis - with China ($14tn) and India ($12tn) not far behind.