In 1990 Kadushin collected data from 127 members of the French financial elite. He used various criteria to determine the top 28 and recorded their who-to-whom responses to questions about who was influencential, who were members of the elite and who were friends. He also recorded a large amount of information on their individual backgrounds and characteristics.
Kadushin, C. 1995. "Friendship among the French financial elite." American Sociological Review 60:202-221.