I’m amazed when people who use Yelp haven’t heard about the Yelp filter! For instance, 20 seconds into the trailer for the forthcoming documentary, Billion Dollar Bully,  several Yelp users are shown on camera saying “Filtered reviews? What are those? Are those the bad reviews?”

The short answer is that all reviews posted on Yelp automatically get screened by Yelp’s in-house filtering software.   This software uses an algorithm to determine which reviews seem to be legit (and those are the ones we get to see), and then “filters” those reviews which appear not to be legit (roughly 25% of reviews).  Interestingly, those reviews which have been filtered and identified as suspicious are still available to readers…but in order to view them, you have to scroll aaaaaaaaaallllllllll the way dowwwwwwnnnnn to the veeeerrrrrry bottom of the business’s listing on Yelp and then click on a small bit of text that says “ [# of] other reviews that are not currently recommended.”  How many users will actually bother to do that?  Probably not too many.

Recently, I came across an interesting study  in the online journal, First Monday, which compared a random sample of filtered reviews and non-filtered, visible reviews on Yelp.  While the author found no linguistic differences between the two data sets, he did find that non-filtered reviews tended to be slightly longer than filtered reviews.  He also found that non-filtered reviews were written by authors whose profiles tended to include photos of themselves (this was much less often the case for the authors of filtered reviews) – and that non-filtered reviews tended to be written by people who were prolific reviewers on Yelp with lots of Yelp friends.  The reviews that had been filtered were often written by a person who had only posted  1 review (or a few), and who had no (or very few) Yelp friends. In a story about Yelp from last week’s local newspaper, a Yelp spokesperson calls these kinds of authors “drive-by Yelpers.”