There is a story in the Wall Street Journal about user ratings on web sites such as Amazon or eBay.  It seems that raters are unduly generous with their stars.

One of the Web’s little secrets is that when consumers write online reviews, they tend to leave positive ratings: The average grade for things online is about 4.3 stars out of five.

And some users are fighting back:

That’s why Amazon reviewer Marc Schenker in Vancouver has become a Web-ratings vigilante. For the past several years, he has left nothing but one-star reviews for products. He has called men’s magazine Maxim a “bacchanalia of hedonism,” and described “The Diary of Anne Frank” as “very, very, very disappointing.”

I have noticed that Amazon reviewers are highly polarized with 5 stars being the most common with 1 star reiews coming in second.  And in fact it makes a lot of sense.  Say you think that a product is over-rated at 4.3 stars and you think that 4 stars is more appropriate.  If there are more than just a few ratings, then to bring the average down to 4 you would have to give the lowest possible rating.

Once enough ratings have already been counted, subsequent raters will be effectively engaging in a tug of war.  Those that want to raise the average will give 5 stars and those that want to reduce it will give 1.