Rand Fishkin posted the best analysis to date of web stats versus online tools to determine a site’s traffic: Website Analytics vs. Competitive Intelligence Metrics, A survey of 25 blogs in the search space comparing external metrics to visitor tracking data.

Despite varying collection methods and numerous flaws in the data that makes it impossilbe to use this information in a quantitative model, this is a must read for anyone who wants to highlight the limitations of these third party marketing intelligence systems. Here is the summary from the SEOMOZ paper:

“This project’s primary objective is to determine the relative levels of accuracy for external metrics (from sites like Technorati, Alexa, Compete, etc.) in comparison to actual visitor traffic data provided by analytics programs. 25 unique sites, all in the search & website marketing niche, generously contributed data to this project. Through the statistics provided, we can also get a closer look at how the blog ecosphere in the search marketing space receives and sends traffic.”

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