Since Marissa Mayer took over as Yahoo's CEO last summer, the portal has been making all kinds of headlines pertaining to its future potential. But last week it made news for topping Google as the web publisher with the most U.S. unique visitors in July, according to research firm comScore.
Per comScore, Yahoo's desktop sites received 196.6 million U.S. unique visitors in July to best Google's 192.3 million uniques. That marks the first time Yahoo has topped comScore's list of U.S. web properties since May 2011. Yahoo has actually come close to overtaking Google a couple times this year, such as May when it was only 667,000 visitors behind Google, but overtaking Google gave it a symbolic lift and certainly generated headlines.
One problem: on a comparison like this, comScore's numbers aren't definitive because they measure Yahoo and Google in different ways.
ComScore bases its traffic measurements largely on panels of U.S. consumers that serve as proxies for the U.S. population, meaning the traffic numbers are estimates projected from those panel members' behaviors.
However comScore can also directly measure publishers' traffic if those publishers allow the research firm to drop what are called census tags on the publishers' sites (think of these census tags are the online equivalent of amusement park turnstiles counting visitors).
Yahoo has adopted these census tags on their properties, but Google has not, according to comScore's VP-industry analysis Andrew Lipsman, who added that comScore designates the level of tagging beside a property's entry in its client interface.
That means that comScore may be able to provide an accurate tally of Yahoo's U.S. traffic but less so when it comes to Google and further means that stacking comScore's numbers for Yahoo and Google against each other may not yield an apples-to-apples comparison.
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 US," emailed a Nielsen spokesperson.
Moreover, none of these metrics count mobile, which can account for 40% to 50% of user visits for some publishers (for Facebook, it's 71%). ComScore is planning to release its combined mobile and desktop metrics in the next few weeks.