Bob Lawson and Jayme Lemke write:
This paper examines travel visa restrictions in 188 countries. We measure travel visa requirements (1) facing foreign visitors into a given country and (2) facing citizens of a given nation traveling abroad. Our analysis shows that countries are more likely to impose visas on foreign visitors when they are large, but less likely when they are rich and economically free. Citizens from richer and more populous countries face fewer travel visa requirements when traveling abroad. Countries are less likely to impose visa requirements on similar nations.