It appears that Airbnb users themselves have bought into the kumbaya, golden halo narrative that has long followed the sharing economy's meteoric rise to mainstream popularity.
A recent academic report out of Boston University found that nearly every single listing on the Airbnb shared accommodation platform has a rating of 4.5 stars or higher.
Yep, that means that 95% of the 600,000 properties surveyed had a rating that was nearly perfect!
Compare this to TripAdvisor, where the survey of nearly half a million hotels found an average rating of 3.8 stars.
They also compared cross-listed properties, and found that more properties received higher reviews on Airbnb than TripAdvisor. So what gives?
Well, maybe Airbnb is just that exceptional and is able to deliver a consistent, memorable experience for nearly every guest. We all know that's just not realistic, especially given anecdotal reports of listings that don't match the photos and host-related nightmares.
So it would seem that the personal, direct nature of the listing service would come into play here. Users feel more empowered to review an anonymous hotel, as it isn't usually tied to an individual.
However, when it comes to reviewing someone after a face-to-face experience (especially one involving that person's home or property), travelers may be much less inclined to rate honestly.
Another factor is likely the age demographics of the site's users.
While concrete, verifiable information on demographics is not disclosed by the companies in question, analyst consensus is that Airbnb skews younger while TripAdvisor skews older. This means that younger users might be less likely to want to criticize or drop ratings on Airbnb.
The authors point to four specific theories for this behavior, as supported by academic literature (emphasis added):

Herding behavior, whereby prior ratings subtly bias the evaluations of subsequent reviewers (Salganik et al. 2006, Muchnik et al. 2013); under-reporting of negative reviews, where reviewers fear retaliatory negative reviews on platforms that allow and encourage two-sided reviewing (Dellarocas and Wood 2008, Bolton et al. 2013, Fradkin et al. 2014); self-selection, where consumers who are a priori more likely to be satisfied with a product are also more likely to purchase and review it (Li and Hitt 2008); and strategic manipulation of reviews, typically undertaken by firms who seek to artificially inflate their online reputations (Mayzlin et al. 2014, Luca and Zervas 2013).
Let's take a look at the rating distribution across accommodation type.
It seems to suggest that self-catering properties might lead to higher satisfaction since the traveler is able to create her own experience as desired. This inherent flexibility and elimination of service hurdles might be one primary reason for the higher ratings of shared and vacation rentals.
Hotels have a much harder job to deliver a consistent, exceptional experience, and also have higher costs than Airbnb listings.
This means that hotels are generally more expensive with more touchpoints that could lead to a less-than-perfect experience. And some cities fare better in the Airbnb vs TripAdvisor ratings game, as the following graphic highlights.
Whatever the reasons for the disparity, it's important for Airbnb users to understand that it exists. There might be a more accurate picture of a particular listing by reading between the lines of the written reviews rather than rely on the star system. It just might tell you all that you need to know!
NB: Airbnb logo courtesy Shutterstock.