Engine Yield

Calculated for each search engine separately, this is how much traffic the engine delivers for every page it crawls.

Each search engine has a different audience size. This metric helps you fairly compare the referral traffic you get from each. In the Netconcepts study, we found that MSN and Yahoo! tend to crawl significantly more pages, but the yield per crawled page from Google is typically significantly higher.

As you optimize your site through multiple iterations, watch the above-mentioned KPIs to ensure you're heading in the right direction. Those not privy to these metrics will have a much harder time capturing the "long tail" of SEO.