There are 3 types of ratings of Untappd:
1) Beer Ratings: These are the ratings that you see on the beer page, wish list, etc. These are now calculated at a PURE average. They are no longer weighted against other beers. To get a rating, a beer must have 10 or more ratings.
2) Brewery Ratings: These are the ratings that appear on the brewery page. These ratings are calculated by providing weight to the highest checked-in beers, and making their ratings count higher than beers with low rating count. The official formula:
(A*Y)+(B*Z)... / (Y+Z).., where A and B are the pure average of the beer, and Y and Z are the check-in counts for a beer.
3) Top Beers: These are the beers you see on the "Top Rated" page on the web and in-app. These ratings, are still done by our old system (Bayesian Average - http://en.wikipedia.org/wiki/Bayesian_average). You must have 150 ratings to qualify for this list. PLEASE NOTE: These ratings for Top Beers are not shown on a Beer page - HOWEVER a beer's weighted rating can be found in-app by selecting "Everyone". The official formula:
$avg_num_ratings // Average number of ratings in all beers $avg_rating // Average rating for all beers $this_num_rating // Number of votes for the beer in question $this_rating // Pure Average Rating for the beer in Question $bayesian_rating = ( ($avg_num_ratings * $avg_rating) + ($this_num_rating * this_rating) ) / ($avg_num_ratings + $this_num_rating);
Ratings are still calculated once per day. Every time you make a rating on Untappd - it will be stored, but the average rating is refreshed on a daily basis.
Frequently Asked Questions about Ratings
When you rate beer on a check-in all previous ratings are averaged up and applied to beer. You can rate as a many times as you want - but you only get 1 rating per beer per user. This cuts down on rating abuse. If you delete a checkin that you rated, that rating will be removed.
You cannot rate a beer a 0. If you do - it's the same as not rating the beer. By not rating a beer, it doesn't count toward it's total. It doesn't mean a 0 rating.
If you have any questions - let us know by opening a discussion at http://untpd.it/newticket.