Thanks. But as skeptical as I am of the extortion claims, I don't see how this study debunks anything. All it does is show that there's no evidence of a systematic bias in the filter, but it doesn't disprove at all that Yelp manually tweaked results in isolated cases, which is what they were accused of.
Here is the one I was referring to: http://officialblog.yelp.com/2013/12/harvard-study-debunks-y...
The myth is that businesses which pay yelp do better; thus yelp extorts businesses to pay.
The study showed that businesses which pay for yelp ads do no better.