China's Provincial PopMigration
Interprovincial migration is a major issue in China due to the mass rural-urban migration that has occured over the last few decades. Measuring interprovincial migration proves to be difficult in all subnational models, simply because the data is frequently lacking and it is rarely available in five-year averages (or with a sufficient time series to generate five-year averages of net migration). In China there is a system to control migration that requires households to register as a means to gain access to services. The system also restricts migration by refusing certain rural households the ability to migrate legally. An unintended consequence of this system is that there is a great deal of illegal migration among the restricted households. Municipalities, such as Beijing, have a substantial migrant worker population which throws off the model's ability to realistically forecast population and age-sex cohorts. Thus, PopMigration is an important series for the China Provincial Model. Tthe national migration registry data is, thus far, inaccessible and it is undoubtedly inaccurate because it does not account for the substantial illegal interprovincial migration.
The current data series in use comes from a paper out of the University of Washington. The author's used a variety of data sources to estimate real interprovincial migration. At this time further research is being done using the paper's appendices to find the original data sources for all the data and understanding the methods used for estimation.