Alexa Makes Big Changes To Traffic Ranking Protocol
Alexa announced the changes in a blog post on Thursday, noting that some users would notice significant changes in their rankings. Although the service has been popular with smaller sites (with unique visitors or page views that don't qualify for inclusion with larger services like Nielsen Online or comScore), critics like TechCrunch's Duncan Riley had long argued that Alexa's reliance on data from toolbar users skewed the results and created biased rankings. One bias, for example, was that the toolbar was unavailable for users of Apple's Mac computers.
As a result of the changes, Alexa rankings data that dates beyond the previous nine months will no longer be available, but the company said has ongoing plans to recalculate the historical info.