Today, where it is pretty easy to “find” supporters to follow or like you on social media networks, raises the question if the wisdom of the crowd is still a reliable measure for ratings. Stated differently, can we still assume that a mean rating of a movie consists of various opinions, or is it too much influenced by planted trends and/or opinions spread on social networks?
In any case, there seems to be a bias towards positive ratings which could be explained by the habit that people who enjoyed a movie are more likely to rate it, why other might think it is not worth it. This is especially true, if ratings are not part of a recommender system which is the case for movie portal or database websites.
But more severe than the problem of imbalanced voters is the missing calibration of user ratings. Plus, the problem that a rating depends on many other non-movie factors, like the mood or the environment. At the end, a group of users gives 5 stars to a movie, but the meaning of the five stars are totally different for each of them. For one, it might mean that a user had a great time, for the other it means the action scenes where top notch, while another one thinks that the effects was very convincing.
In combination with the expectations raised due to ads or social media, users might focus on only specific aspects that were endorsed while at the same time intentionally ignoring existing flaws. Of course this is just a theory, but we cannot deny that advertising and opinion making has been considerably changed in the last years and it is only logical to assume that this also influences the way users are rating movies.