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