PHP/MySQL - algorithm for "Top Rated"

Question

So I just built a star-rating system and and trying to come up with an algorithm to list the "Top Rated" items. For simplicity, here are the columns:

item_name
average_rating (a decimal from 1 to 5)
num_votes

I'm trying to determine the "sweet spot" between number of votes and rating. For example...

• An item rated (4.6 / 20 votes) should be higher on the list than an item that's (5.0 / 2 votes)
• An item rated (2.5 / 100 votes) should be below an item that's (4.5 / 2 votes)

So in other words, num_votes plays a factor in what's "Top".

Anyone know of an algorithm that is pretty good at determining this "sweet spot"?

Thanks in advance.

Answer 1

here's another, statistically sound good way: http://www.thebroth.com/blog/118/bayesian-rating

Answer 2

The question is, how much higher the 4.6/20 shall be rated than the 5.0/2...

An idea not to take items in consideration that do not have at least x votes.

Another idea is to fill up with "medium" votes. Decide that 10votes shall be the minimum. The 5.0/2 must be filled with 8 virtual votes of 2.5

5.0/2 means 2 votes with 5.0, add 8 with 2.5 you'll get 30/10 -> 3.0 ;)

Now, you have to decide how many votes an item shall at least have. For those that already have the minimum votes, a direct comparation shall be done.

4.5/20 > 4.4/100
5.0/2  < 3.1/20  (as 5.0/2 is, as we calculated, 3.0/10)