bayesian averages and aggregates

trying to resolve the age old problem of items with few votes climbing to the top based on average votes. total points isn't bad as a surrogate for more complex calculations, but it isn't great either.

the bayesian formula as follows take into account the average number of votes every item received, and the average rating of every item using that to weight against this item.

br = ( (avg_num_votes * avg_rating) + (this_num_votes * this_rating) ) / (avg_num_votes + this_num_votes)

obviously to implement, this would have to be coded as a relationship. where would i look for the appropriate code to edit? hacking into the total points relationship would probably be the quickest way. thanks for your help.