China has had the world's largest middle class population since 2015, and the middle class grew to a size of 400 million by 2018. In 2020, a study by the Brookings Institution forecast that China's middle-class will reach 1.2 billion by 2027 (almost 4 times the entire U.S. population today), making up one fourth of the world total. Wages in China have grown a lot in the last 40 years—real (inflation-adjusted) wages grew seven-fold from 1978 to 2007. By 2018, median wages in Chinese cities such as Shanghai were about the same as or higher than the wages in Eastern European countries. China has the world's highest number of billionaires, with nearly 878 as of October 2020, increasing at the rate of roughly five per week. China has a high level of economic inequality, which has increased in the past few decades. In 2018 China's Gini coefficient was 0.467, according to the World Bank.