  Airbnb, an online marketplace for accommodations, has experienced a
staggering growth accompanied by intense debates and scattered regulations
around the world. Current discourses, however, are largely focused on opinions
rather than empirical evidences. Here, we aim to bridge this gap by presenting
the first large-scale measurement study on Airbnb, using a crawled data set
containing 2.3 million listings, 1.3 million hosts, and 19.3 million reviews.
We measure several key characteristics at the heart of the ongoing debate and
the sharing economy. Among others, we find that Airbnb has reached a global yet
heterogeneous coverage. The majority of its listings across many countries are
entire homes, suggesting that Airbnb is actually more like a rental marketplace
rather than a spare-room sharing platform. Analysis on star-ratings reveals
that there is a bias toward positive ratings, amplified by a bias toward using
positive words in reviews. The extent of such bias is greater than Yelp
reviews, which were already shown to exhibit a positive bias. We investigate a
key issue---commercial hosts who own multiple listings on Airbnb---repeatedly
discussed in the current debate. We find that their existence is prevalent,
they are early-movers towards joining Airbnb, and their listings are
disproportionately entire homes and located in the US. Our work advances the
current understanding of how Airbnb is being used and may serve as an
independent and empirical reference to inform the debate.
