Why do China college students go to Europe and the United States to study for doctoral masters, which belongs to population migration?

The so-called "population migration" is a form of population mobility, which refers to the change of population distribution in spatial position. Generally speaking, it refers to the spatial flow of population between two regions, which usually involves the permanent or long-term change of population residence from the place of emigration to the place of emigration. Due to different research angles, there are many definitions of the concept of population migration in academic circles. The United Nations Multilingual Demography Dictionary gives a generally accepted definition of population migration, that is, "the geographical or spatial movement of population between two regions usually involves the change of permanent residence from the place of emigration to the place of immigration. This kind of migration is called permanent migration, which is different from other forms of population mobility that do not involve changes in permanent residence. " This concept leads to two important characteristics of population migration:

(1) Time attribute of population migration. In other words, only those flows with "permanent" changes in residence can be called population migration, while the changes in temporary residence caused by daily commuting activities are excluded.

(2) Spatial attributes of population migration. That is, population migration must move out of the original place of residence for a certain distance, generally on the premise of crossing administrative boundaries, thus excluding people who change their places of residence in the same administrative area.