Top 20 ranking uses Bayesian Ratings:
Bayesian ratings prevent items with a small number of potentially inaccurate rankings from ranking in especially high or low spots. For example, without Bayesian ratings, an item with only 2 five star ratings would outrank an item with 20 four star ratings and 1 five star rating. An item with a single one star rating would rank lower than an item with 20 two star ratings and 10 one star ratings.
