Ad Age‘s Tim Peterson dug a little deeper in the wake of all that yodeling about Yahoo having surpassed Google for the first time in two years in monthly U.S. unique visitor traffic.
The reporter explains that only Yahoo has comScore “census tags” affixed to its sites. What this means is that for July, the immediate Yahoo numbers came from a much more extensive and specific pathway than those of Google, which were calculated using the more traditional method of a comScore “panel” that was then extrapolated. From Peterson’s piece:
comScore’s methodology likely explains why Nielsen, which relies only on panels for its traffic measures, sees a greater gap between Google and Yahoo and not in Yahoo’s favor. “During July 2013 we measured Google as the top parent company for web activity (170M unique US visitors) and Yahoo as the ranked fourth (126M unique US visitors) in the U.S.,” emailed a Nielsen spokesperson.