As described in the university ranking section, it is not easy to obtain and standardize data from 1 countries, 218 universities/ institutions for the country ranking. Therefore, we based our ranking system on the number of meritorious scientists. Four criteria are used to rank the countries. The first one is the number of scientists in the top 3 % list. The second criterion is the number of scientists in the top 10%, Top 20%, Top 40%, top 60% and top 80% list. The third one is the number of scientists listed in the AD Scientific Index. In the case of equalities after applying all these three criteria, the world rank of the meritorious scientist of that country is used. See also: University Subject Rankings,  All Universities, Private Universities, Public Universities, Institutions, Companies and Hospitals