The Impact Mechanisms of Players’ International Migration on National Team Performance

national team level use by World Football ELO rating (http://www.eloratings.net/), player imports represent the number of foreign players in each country/region's top-tier league, and player exports represent the number of exported players in each country/region's top-tier league (https://www.transfermarkt.co.uk/).Youth team level is measured by teams’ performance in U17/U20 World Cup(https://www.fifa.com). League level is the International Federation of Football History and Statistics' strongest national league ranking (https://www.iffhs.com/). Since only about top 80 rankings are published each year, leagues no rankings are assigned minimum value of 100.population and economy (https://www.worldbank.org/en/home/).