## A bayesian cinefeel…(*)

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.