According to a study titled Anonymity, Social Image, and the Competition for Volunteers: A Case Study of the Online Market for Reviews, by economics professor Zhongmin Wang, Yelp.com offers the most balanced business reviews when compared to those of Citysearch and Yahoo Local.
The findings show the proportion of 5-star ratings at Yelp (24.4 percent) is less than that at Citysearch (50.3 percent) or Yahoo Local (58.8 percent). The same holds true for 1-star ratings, with Yelp showing proportions of 5.9 percent, compared to Citysearch (16.4 percent) and Yahoo Local (6.9 percent). In other words, where Yelp is more balanced, Citysearch and Yahoo are more extreme.
Another interesting finding was that Yelp reviewers are much more active. Just 9 percent of Yelp reviewers had posted only one review. Compare that to Citysearch, where 71 percent of users posted only one review, and Yahoo Local (56 percent).
As business owners, it appears that Yelp is the place where you can get the fairest, most trusted reviews of your business. Not only is this important for your own research purposes but also a sign that Yelp is trusted by other consumers, making it a site that must be monitored. On the other end, Citysearch and Yahoo Local might not be as popular, but be on the lookout for extreme reviews.
The entire study can be found here.