Author attributes it to the fact that reviewers are anonymous at CitySearch and Yahoo local, but build up reputations on Yelp. Of course, there are also other differences between the sites.
Zhongmin Wang (2010) “Anonymity, Social Image, and the Competition for Volunteers: A Case
Study of the Online Market for Reviews,” The B.E. Journal of Economic Analysis & Policy: Vol.
10: Iss. 1 (Contributions), Article 44.
Available at: http://www.bepress.com/bejeap/vol10/iss1/art44
This paper takes a ﬁrst step toward understanding the working of the online market for re-
views. Most online review ﬁrms rely on unpaid volunteers to write reviews. Can a for-proﬁt
online review ﬁrm attract productive volunteer reviewers, limit the number of ranting or raving
reviewers, and marginalize fake reviewers? This paper sheds light on this issue by studying re-
viewer productivity and restaurant ratings at Yelp, where reviewers are encouraged to establish a
social image, and two competing websites, where reviewers are completely anonymous. Using a
dataset of nearly half a million reviewer accounts, we ﬁnd that the number (proportion) of proliﬁc
reviewers on Yelp is an order of magnitude larger than that on either competing site, more produc-
tive reviewers on all three websites are less likely to give an extreme rating, and restaurant ratings
on Yelp tend to be much less extreme than those on either competing site.