The study takes a look at all filtered reviews, which Yelp identifies as fake through a series of algorithms. Users can still see filtered reviews, but they have to dig around with the settings, the study notes.
"What does a filtered review look like? We first consider the distribution of star-ratings. The data show that filtered reviews tend to be more extreme than published reviews. This observation relates to a broader literature on the distribution of opinion in user-generated content," the study says.
Overall, the study analyzed restaurants in Boston, looking at "every Yelp review that was written from the founding of Yelp in 2004 through 2012, other than the roughly 1 percent of reviews that violate Yelp's terms of service." This resulted in filtering through 316,415 reviews for 3,625 restaurants. Of all 316,415 reviews, 50,486 were faked, according to Yelp's standards. And that's not even counting the fake reviews that slip through the cracks.
Of course, this doesn't even begin to discuss the multiple problems of Yelp, not only the fake reviews and nonexistent restaurants that live, unfiltered, on the user-generated review site, but also the business' policy of demanding restaurants pay for advertising.
Of the reviews that Yelp caught, however, the study found that most of the time, fake positive reviews were created to up the restaurants' reputation, while negative reviews were posted on competitors' pages. A small percentage of them, we're sure, are meant as jokes (see: Stefan K.)