There’s an interesting post over at the Search Engine Roundtable Forums about the reliability of Google Analytics data versus data generated by Urchin 5.7 software. Barry Schwartz points out a 20% hike in traffic stats through Urchin when viewing data for one of his sites.

It’s important to remember that different web analytics products may use various means to track visits to your site. If you opt to run two analytics packages simultaneously, be prepared for discrepancies in your reports. Google Analytics uses a script-based method to gather traffic stats, while Urchin relies primarily on your server logs. Many bots count as hits on these server logs, but don’t trigger the JavaScript tracker. They’ll pass undetected through Google Analytics, but clamber through your site just like a human user would, at least according to an Urchin install that relies entirely on web server logs.

Another Roundtable forum member put Google Analytics and Urchin to the test and found some rather interesting results: Urchin, with the optional UTM feature enabled, and set to log cookies, produced data that differs from Google Analytics by a mere ~0.5%.

The vast majority of actual human beings hitting your site will have JavaScript enabled (at least 90%, as of July 2005, according to the W3Schools Browser Stats page), so anyone who might actually trigger a sale or a conversion will be counted by script-based tracking, as used by Google Analytics or Urchin’s UTM.