the inland-coastal contribution has increased by several fold,” meaning that inland-coastal inequality is playing an increasingly important role in the formation of general income inequality across China. A study found that variations across Chinese provinces account for about 12% of the country's overall income inequality. Research on economic growth after the opening of the Chinese economy has shown that between 1989 and 2004, income in coastal provinces more than tripled whilst that in inland provinces doubled. Research on inland-coastal inequality indicates that "since being a coastal province is a geographic advantage that will persist, this tendency for divergence will also probably continue," but institutional factors still have a significant effect. Economists Ravi Kanbur and Xiao Zhang propose that the “greater ease of rural-to-urban migration within provinces, compared to the institutional and other difficulties of migrating from inland to coastal provinces” can partially explain this phenomenon. China's Hukou system (户口) is an institutional factor that significantly inhibits interprovincial migration. Recently, the government has introduced policies that relax Hukou related restrictions in small and medium-sized cities, in an effort to encourage growth. “Currently rural incomes are less equally distributed than urban incomes but urban inequality is increasing faster than rural inequality” (Wu, 2005, p. 773). Education According to research conducted at the World Bank, “inequality of access to education is an important source of inequality in China across people contemporaneously and across generations.” In fact, “a decomposition analysis based on household income determination shows that the largest proportion of changes in total income can be attributed to the increase in returns to education.” Urban-biased policies and inland-coastal inequality exacerbates the issue of education inequality in China. One of the primary issues is their generation of sector-biased income transfers and expenditures on health, housing and education, which "not only distort economic incentives of the workers in the sectors, but will also affect the human-capital attainments of their children, which may further widen the rural-urban income gap." In other words, inland and rural inequality can help create a vicious cycle by funneling money towards the coastal cities and away from investments in human capital elsewhere. Like in the United States, education funding is primarily the responsibility of local governments in China. As poor localities are less able to fund these services and poor households are less able to afford the high private cost of basic education, China has seen an increase in the inequality