世界银行是怎样对各国进行分类的，看看这三个网站或许有帮助！
https://datahelpdesk.worldbank.org/knowledgebase/articles/378834-how-does-the-world-bank-classify-countries

https://datahelpdesk.worldbank.org/knowledgebase/articles/378832-what-is-the-world-bank-atlas-method

http://data.worldbank.org/about/country-and-lending-groups

同时附上一份国家分类的历史数据