Google is rather non-descript about what “past performance” means in this context. Our well-trained PPC minds automatically reference CTR as the primary means to determine performance, but when talking about the Conent Network, there are other factors at play.

For determining Quality Score for keyword-targeted ads on the Content Network, Google is looking at what I would label as “relevancy performance.” They’re all about seeing how an ad performs (which I’m confident includes CTR in part) on an individual site, or related sites. So if your ad gets a ton of clicks on “celebrity gossip site A” – Google will take that past performance and automatically assume that your ad will also get a ton of clicks on “celebrity gossip site B.”

I don’t think that they specificaly say that CTR isn’t a factor, just that it’s not the ONLY factor. Hope that helps make sense of all this!

Just a specific question concerning content (excluding placement targeted) performance history — how does Google gauge how well an ad is performing? On one hand, they claim that they do not factor in CTR for content quality score (as seen here: http://adwords.google.com/support/bin/answer.py?answer=10215&topic=9354). On the other, they go by ‘past performance’ (as seen here: http://adwords.google.com/support/bin/answer.py?answer=6111&topic=7093).

Thanks in advance,
Benjamin