The movie UMA VIDA SUBLIME hat a movie rating of 6,2 with 99 votes. Then, someone vote 7, and the movie rating then down to 5.9. ??? How is it possible?
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Posted 1 year ago
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First, the overall rating is not the arithmetical mean of all registered rating. IMDb has a mysterious secret formulae that takes care of several factors, e.g. excluding rates from non registered voters. Some legit voters may also change there ratings (I can do it if my opinion on a movie has changed when watching it again). And maybe other reasons that IMDb would not disclose.
My belief is that there is a computation formulae, which is consistent for all entries.
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You just cannot have a formula where you go down after a vote that foes up. And the secret formula cannot be an excuse because the truth is thar now I don't know if they make it on purpose. Is imdb credible os are they controled by other values. They put Uma Vida Sublime down 4 days before it opens in cinema. Just a coincidence?
Someone should investigate this.
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I do not say that this is what happened, but mathematically speaking, it could happen.
In any case, I do not think IMDb will share any investigation, if any: absolutely all requests regarding the change of ratings and overall computation have always been ignored...
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Reply to Vincent Fournols
IMDb has a mysterious secret formulae
  
I do not understand any of this  You want to play with the Numbers ? ?
https://en.wikipedia.org/wiki/IMDb
https://en.wikipedia.org/wiki/IMDb#User_ratings_of_films
W = R.v+C.m

v+m
where:
W = weighted rating
R = average for the movie as a number from 1 to 10 (mean) = (Rating)
v = number of votes for the movie = (votes)
m = minimum votes required to be listed in the Top 250 (currently 25,000)
C = the mean vote across the whole report (currently 7.0)
The W in this formula is equivalent to a Bayesian posterior mean (see Bayesian statistics).
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Col Needham, Official Rep
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However, we can add one more piece of detail for this case since the answer is right in front of everyone's eyes. For titles < 100 votes, the weighted average is the arithmetic mean; once a title hits 100 valid votes (or more) the IMDb weighted average formula kicks in.
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Next time with 99 votes i will ask people not to vote more. Eh, eh. Or if i ask someone to delete his vote the average will go up? Strange
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Watch what happens when one of these guys votes on a movie with a low vote count.
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Col Needham, Official Rep
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Insignificant fractions are not used.
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