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