Question about IMDB

[Miss Chicken]

Does anyone worked out how they reach the "weighted average" of a movie on Internet Movie Database? Do you think the 'weighted average" is a fair indication of how good a movie is?

I just looked up one of my favourite movies, Orphans, on IMDB. Its averages are as follows. (after being rated by 523 users)

Median - 8
Arithmetic mean - 7.5
Weighted average - 6.5

On Amazon this movie gets 5 stars after 19 people rated it 5 stars and 2 people rated it 3 stars.

 

[CaptainCanada]

The weighted mean is some formula to try and prevent the rating from being hijacked, though they're quite secretive about how it works in order to prevent people from trying to work around it.

 

[Harvey]

The formula can be found on the IMDB page on Wikipedia, although there are certain aspects of the calculation (i.e. how active a user must be to be considered a regular voter) that are kept secret: http://en.wikipedia.org/wiki/Internet_Movie_Database