$avg_num_votes = 18; // Average number of votes in all products
$avg_rating = 3.7; // Average rating for all products
$this_num_votes = 6; // Number of votes for this product
$this_rating = 4; // Rating for this product
$bayesian_rating = ( ($avg_num_votes * $avg_rating) + ($this_num_votes * this_rating) ) / ($avg_num_votes + $this_num_votes);