Internal migration in the People's Republic of China is one of the most extensive in the world according to the International Labour Organization. In fact, research done by Kam Wing Chan of the University of Washington suggests that “In the 30 years since 1979, China’s urban population has grown by about 440 million to 622 million in 2009. Of the 440 million increase, about 340 million was attributable to net migration and urban reclassification. Even if only half of that increase was migration, the volume of rural-urban migration in such a short period is likely the largest in human history.” Migrants in China are commonly members of a floating population, which refers primarily to migrants in China without local household registration status through the Chinese Hukou system. In general, rural-urban migrant workers are most excluded from local educational resources, city-wide social welfare programs and many jobs because of their lack of hukou status.