  Yelp ratings are often viewed as a reputation metric for local businesses. In
this paper we study how Yelp ratings evolve over time. Our main finding is that
on average the first ratings that businesses receive overestimate their
eventual reputation. In particular, the first review that a business receives
in our dataset averages 4.1 stars, while the 20th review averages just 3.69
stars. This significant warm-start bias which may be attributed to the limited
exposure of a business in its first steps may mask analysis performed on
ratings and reputational ramifications. Therefore, we study techniques to
identify and correct for this bias. Further, we perform a case study to explore
the effect of a Groupon deal on the merchant's subsequent ratings and show both
that previous research has overestimated Groupon's effect to merchants'
reputation and that average ratings anticorrelate with the number of reviews
received. Our analysis points to the importance of identifying and removing
biases from Yelp reviews.
