Shaddows - 1:27 pm on Mar 8, 2011 (gmt 0)

I think we should split this off. That PDF is a goldmine.

Even ignoring the maths, it contains such nuggets as

We measure the performance of PLANET on the bounce rate prediction problem [22, 23]. A click on an sponsored search advertisement is called a bounce if the click is immediately followed by the user returning to the search engine. Ads with high bounce rates are indicative of poor user experience and provide a strong signal of advertisement quality.

So, there you go. And yes I know, Adverts and organics use different algos. And if an advert bounces as defined, the page almost certainly did NOT serve its purpose, which is less clear from organics (where a question might have been suitably answered, for example).