The answer is "there are striking differences in sexual experience within the U.S. population".
Laumann is known for his spearheading work in a many zones of sociology. He is one of the authors of the field of social network analysis, and kept in touch with a portion of the foundational work at systems of elites, hierarchical systems, and egocentric systems. He is similarly outstanding for his work in the sociology of sexuality, both for his hypothetical and exact commitments to the field and for his years-long battle against Congress for assets to gather national information on American sexual standards and practices in the wake of the AIDS emergency.