Googler Criticizes Alexa Data

Peter Norvig, director of research at Google, has published some stats showing what many online marketers have been saying for years -- Alexa data is skewed by the fact that more online marketers download the Alexa toolbar.

Alexa has come under fire repeatedly in recent years, from marketers and competitors.

Norvig's limited test with five tech sites shows that Alexa creates as much as a 50:1 selection bias for certain sites, such as that of Matt Cutts, who discusses the stats on his blog. Because more search marketers tend to download Alexa's toolbar, Cutts has an Alexa pageview ranking that's about 25 times that of Norvig, though actual server stats show that Norvig's site gets nearly twice the pageviews.

"What that means is that people with the Alexa toolbar installed are 25 times more likely to view a page on Matt's site versus mine, but overall, all users view twice as many pages on my site," he writes.

About the author

Kevin Newcomb joined ClickZ in August 2004, covering search marketing and other online marketing topics. He has been reporting on web-based businesses since 2000.

Before the bubble burst, Kevin was a marketing manager for an online computer reseller, handling copywriting, e-mail marketing, search marketing and running the affiliate program.

With a combination of real-world marketing experience and years of business journalism, Kevin brings to ClickZ a unique ability to deliver news and training materials that help online marketers do their jobs better.