 The Chinese government estimates that of the 1,200,000 Chinese people who have gone overseas to study in the thirty years since China's economic reforms beginning in 1978; three-quarters of those who left have not returned to China.The usage of Chinese by the overseas Chinese has been determined by a large number of factors, including their ancestry, their migrant ancestors' "regime of origin", assimilation through generational changes, and official policies of their country of residence.The general trend is that more established Chinese populations in the Western world and in many regions of Asia have Cantonese as either the dominant variety or as a common community vernacular, while Mandarin is much more prevalent among new arrivals, making it increasingly common in many Chinatowns.