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.
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.
here's another, statistically sound good way: http://www.thebroth.com/blog/118/bayesian-rating
How about you give each 10 votes a weight of 1 so 20 votes gives the item 2 weight. Then if the item has 0 weight it will loose 0.5 from the average