selecting content for and distributing content to {HEAD ~ users} based on {TAIL ~ their association} with the affinity group 
based on
selecting content for and distributing content to { HEAD ~ users } based on { TAIL ~ their association } with the affinity group
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH