I was just surfing around on IMDB, and saw the ratings breakdown for a movie called Roadside Prophets. Clearly the user votes fall heavily on the upper end of the 1 to 10 scale, yet the ratings average remains, oddly, at 5.7. Given the breakdown of the votes, shown on this page, this score seems unfairly negative and strongly mathematically unrepresentative of the votes. IMDB has a page that explains the mysterious “filtering” process it uses to thwart “ballot-stuffing,” but in the context of the user voting records, it seems like this 5.7 score will wrongly dissuade people from watching a movie that has gotten overwhelmingly positive ratings. Does this vote tampering on IMDB’s part make sense, and moreover, does this filtering process raise the average of mediocre movies and reduce the average of very good movies?
Without knowing how the IMDb weighted average works, it’s impossible to say how valid it is.
However, I suggest that you take a look at the second bar chart at the bottom of the page. The breakdowns are only for about 175 people. And they all do cluster around the 5.7 mark. Apparently, IMDb removed a full 150 or so votes they considered to be fraudulent. That many votes stuffed into the total would wildly raise the overall average.
Again, there is no way to know why these particular votes were removed and therefore no way to tell whether the process works or not. Giving IMDb the benefit of the doubt, however, they did a good thing.