by manos_parzakonis

How imbd ranks movies?

The formula for calculating the Top Rated 250 Titles gives atrue Bayesian estimate:

- where:*

= average for the movie (mean) = (Rating)

= number of votes for the movie = (votes)

= minimum votes required to be listed in the Top 250 (currently 1500)

= the mean vote across the whole report (currently 6.9)

- for the Top 250, only votes from regular voters are considered.* (source)

Now that’s something unexpected! Going further than the simple arithmetic mean is something exciting, right?

The formula is the well-known decomposition of the posterior mean -distributed a priori as normal- compromising the prior guess () and the data () weighted by the sample () and the pretend-to-be initial sample () under the conjugate prior setting.

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