Impact of English Proficiency on National Prosperity: Comparative Study on the Outer Circle and the Expanding Circle

English has become an international language, with a large number of governments promoting its study for national prosperity and economic development. However, there have been only a few empirical studies concerning the impact of English proficiency on the economic development of countries. These studies utilize economic development indicators such as GDP, GDP per capita, as well as GDI. They also adopt various English proficiency indicators: average TOEFL scores, average EF Standard English Test scores, and a comparison of the Outer Circle and the Expanding Circle. They focus on the influence of English proficiency on economic development and foreign trade, but not on prosperity, which consists of some elements other than these. Furthermore, results in this field significantly change depending on the types of indicators. Therefore, further research is necessary with various indicators to draw a more complete picture. This study adopts the Legatum Prosperity Index as a prosperity measurement and compares the Expanding Circle and the Outer Circle with a t-test. The result shows that the former is superior to the later. The study further investigates the situation in Asia and Africa, since these regions have a significant number of Outer-Circle countries. The research outcome indicates that there is no significant statistical difference between the two circles. These results suggest that having a large number of people who have high English proficiency does not always lead nations to prosperity.