[grandalf]

Excellent point. Per your question I'm also curious if there is a way to make aggregate ratings more useful as a quality measurement.

For instance, if I see a product on Amazon with a 4.8 average rating but notice a lot of very angry 1 star ratings, I'm likely to infer that there may be quality control problems.

Amazon displays a histogram so the shopper can assess the meaning of the distribution heuristically.

There's also the issue of whether ratings should be absolute or based on value. If I buy some obviously knockoff ear buds for $6 and they are way better than expected, I'd give them 5 stars, but if they had cost $50 I'd have given a three star review.

So for shopping it seems that there are multiple signals being aliased into a single star rating.

[paulgb]

Somewhat related, I think it was Nate Silver who theorized that given enough time all restaurant reviews trend towards four stars. The theory is that if something gets less than four stars it attracts a niche crowd that appreciates it uniquely (and rates highly), while if it gets five stars it attracts a general crowd that doesn't have a particular appreciation (and rates poorly).

[ghaff]

And/or restaurants that everyone hates tend not to stay in business. There's also a more general effect that ratings (and reviews) affect the behaviors of people who haven't rated yet. I wouldn't rate many movies that I see below a 3/meh/OK level. That's not so much because I grade inflate but because I actively seek to avoid movies I'd rate 1 or 2 (and, indeed, mostly 3).