In 1965 Hofstede founded the personnel research department of IBM Europe (which he managed until 1971). Between 1967 and 1973, he executed a large survey study regarding national values differences across the worldwide subsidiaries of this multinational corporation: he compared the answers of 117,000 IBM matched employees samples on the same attitude survey in different countries. He first focused his research on the 40 largest countries, and then extended it to 50 countries and 3 regions, "at that time probably the largest matched-sample cross-national database available anywhere."[3] The theory was one of the first quantifiable theories that could be used to explain observed differences between cultures.[citation needed]