Complex sentence: Most research on hookups has been focused on American college students, but studies show that upwards of 60% or 70% of sexually active teens in some North American surveys reported having had uncommitted sex within the last year.
Split into simpler sentences: Most research on hookups has been focused on American college students, but hookups are not limited to college campuses. Studies show that upwards of 60% or 70% of sexually active teens in some North American surveys reported having had uncommitted sex within the last year.