By Evan Miller February 6, 2009 ( Changes ) PROBLEM : You are a web programmer. You have users. Your users rate stuff on your site. You want to put the highest-rated stuff at the top and lowest-rated at the bottom. You need some sort of "score" to sort by. WRONG SOLUTION #1 : Score = (Positive ratings) - (Negative ratings) Why it is wrong : Suppose one item has 600 positive ratings and 400 negative ratings: 60% positive. Suppose item two has 5,500 positive ratings and 4,500 negative ratings: 55% positive. This algorithm puts item two (score = 1000, but only 55% positive) above item one (score = 200, and 60% positive). WRONG. Sites that make this mistake : Urban Dictionary WRONG SOLUTION #2 : Score = Average rating = (Positive ratings) / (Total ratings) Why it is wrong : Average rating works fine if you always have a ton of ratings, but suppose item 1 has 2 positive rati...