We use a weighted calculation to compute the average rating for each film, rather than a straight mean of all the ratings cast. Only one rating is considered per member (specifically, the most recent rating that the member cast for the film).
The “weighted” part of the calculation refers to the mechanism we use to compute the average. Every rating cast after a film’s release is considered, with weightings applied based on the number of ratings the film has received and other heuristics. For example, a film with only a handful of five-star ratings has its average weighted down to account for its lower volume of ratings compared to a film with tens or hundreds of thousands of ratings. Our approach also identifies unusual patterns of rating activity and accounts for these in the final score. (We do not disclose the specifics of our weighting approach, in order to protect its integrity.)