If you were an advertiser, you might have read the news last week that Yahoo had supplanted Google as the number one web property in the US and decided to shift your dollars. ComScore's monthly ranking of "top US web properties" listed Yahoo as number one for the first time since 2011. Even though its numbers are unverified, ComScore is the industry standard for web traffic metrics; as far as advertisers are concerned, what it says goes.

But additional data from ComScore as well as analytics firms Compete and SimilarWeb suggest that Yahoo is still far behind Google — and that third-party data analytics should be taken with a big grain of salt.

ComScore's ranking tracked unique visitors rather than unique views, so repeat traffic from the same user would have been discounted. That means all those 13-year-old Justin Bieber fans are only counted once a month, even if they watch the video for "Baby" five times a day and spend three hours every night reading Belieber posts on Blogger.

Third-party data analytics should be taken with a big grain of salt

When looking at unique visitors, Yahoo sites and Google sites were neck and neck, with Yahoo slightly ahead: 196,564,000 visitors versus 192,251,000. Those numbers were close enough to attribute to normal month-month variability, but it was the first time Yahoo had surpassed Google since 2011, so it made a big impact. If ComScore added in Tumblr, which Yahoo recently acquired, it might have given the company a stronger margin.

That was just for the US. Globally, ComScore estimates that Yahoo sites got 724 million unique visitors a month in July while Google sites got 1.2 billion unique visitors, showing that the search giant is still the bigger force around the world.

But can you really trust ComScore numbers? Data from Compete, which only includes sites on the yahoo.com and google.com domains, shows Yahoo with around 165 million unique visitors in July and Google with 170 million (Google wins). Switch to unique visits, and Compete says Yahoo has 2.2 billion while Google has just over 2 billion (Yahoo wins).

SimilarWeb, which included Tumblr and YouTube in its data, gave Google sites 9.4 billion visits in the US while Yahoo sites received just 2.4 billion (Google wins). The disparity between the two companies widened when SimilarWeb looked at global traffic in addition to US traffic. Yahoo showed only 6.8 billion visits while Google has 41.2 billion monthly visits (Google wins, by a mile).

These companies all measure desktop web traffic only; the numbers would likely change a lot if traffic from mobile devices was included. The firms also all use different methodologies for estimating their numbers, but Yahoo came out ahead only when the data was restricted to unique users in the US. In almost every other scenario, Google was the clear winner.

Still, it's mostly good news for Yahoo

Still, it's mostly good news for Yahoo, where traffic has been waning over the past few years. Yahoo CEO Marissa Mayer, who took the job a year ago, said in a second-quarter investor call that the company has reversed traffic declines and started to grow.

"Renewed traffic growth in the face of multiple years of decline is, to my knowledge, unprecedented among industry players that operate with billions of page views," Mayer said on the earnings call last week. "And we've achieved just that." Yahoo told The Verge it does not comment on third party analytics, and it was impossible to use third party analytics to fact-check Mayer's claim: they all showed different trends for Yahoo's traffic, including up, down, and flat, depending on the firm and the metric.

But even Mayer says the gains are modest: the company only reversed its declines and started hitting new traffic records in early June. Whether the third-party stats are accurate or not, it seems that its researchers and Mayer are in agreement: Yahoo has a long way to go.

Nathan Ingraham contributed to this report.