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Sun, Jan 20, 2019 1:15 PM

Movie rating.

Why movie rating goes down with a vote that goes up?
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? 

Responses

6.4K Messages

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157.2K Points

2 years ago

Interesting.

2.4K Messages

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80.9K Points

2 years ago

Hi Luis,

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.

4 Messages

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210 Points

Thanks. But in this case doesn't really makes sense because no ond changed vote. It was a vote of 7.
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.

2.4K Messages

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80.9K Points

Not necessarily: you show us two snapshots, one with 99 votes, one with 100, with almost exactly the same breakdown. But actually you may have had -4+5 and these 9 gap votes may impact the overall rating differently.
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...

4.2K Messages

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133.7K Points

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).
.

2.4K Messages

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80.9K Points

I fully trust you, ACT! :D

4.2K Messages

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133.7K Points

If I said I was a liar - would I be telling you the truth ? ?
.

2.4K Messages

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80.9K Points

It depends on the stakes... ;)

4 Messages

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210 Points

9 gap votes??? There is just one vote more . What's the doubt about this? Just one more person voted 7. Is pure math: you cannot have your average down with a new higher vote.

2.4K Messages

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80.9K Points

No, it is one more aggregated votes, but you do not know how many could have been removed (for whatever IMDb reason) when the same number plus one being added. And maybe among these latter ones, some do not qualify to be computed into the overall rating. So the breakdown by votes, and any change between two snapshots can hardly give any clue on the way the overall rating will change.

6.4K Messages

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157.2K Points

As Vincent Fournols suggested, it is possible that a VIP swapped votes with a non-VIP, so to speak. Am I making sense? And as ACT_1 suggested, it is not the formula that is proprietary but the the identities of voters along with whether or not their votes are weighted, how much and how the weight assignment to the voter was determined.

Employee

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4.1K Messages

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140.1K Points

2 years ago

Thank you for sharing your concern, generally all we can say about voting is covered in the FAQ at https://help.imdb.com/article/imdb/track-movies-tv/faq-for-imdb-ratings/G67Y87TFYYP6TWAV

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. 

2.4K Messages

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80.9K Points

Thanks Col, this is interesting to know.

6.4K Messages

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157.2K Points

O, yeah...

4 Messages

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210 Points

Thanks. That is a explanation I can accept. But of course could not be the formula.
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

14 Messages

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382 Points

It’s generated as a median of the whole votes, so if you had 10 people vote 5/10, the median would be 5. If 6 of them voted 4/10, the rest voted 6/10, the median would be 4.

14 Messages

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382 Points

Why are commas used instead of full stops when showing fractions? I. E. 6,2 rather than 6.2