Stanley lieberson’s research on first names in the united states focused on which phenomenon?

Stanley Lieberson's exploration on first names in the United States centered the expansion of one of a kind names among blacks beginning in the 1960s. 
Stanley Lieberson and Kelly Mikelson gave subjects a rundown of special names they found in the Illinois database to check whether the subjects could effectively distinguish the sexual orientation of the genuine youngster. Most by far could effectively recognize the sexual orientation of the genuine tyke.

6, 4, 5, 1 are true. the others are false.