Variations in {HEAD ~ differences} between target web site data values and corresponding average and bounding web site data values over time determines improvement and {TAIL ~ success} of the target web site 
Variations in { HEAD ~ differences } between target web site data values and corresponding average and bounding web site data values over time determines improvement and { TAIL ~ success } of the target web site
OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH