This image explains how Reddit's Ranking algorithm works.
As you know, Reddit is a very high traffic site. Therefore, the post rank decreases quite fast. This algorithm puts emphasis on bringing newer posts to the top faster. For websites with low traffic, low frequency of posts and especially low number of upvotes and downvotes, it would make more sense to slow this process down a little. Any ideas? (I am not a mathematician :( ). The algorithm has been discussed in some detail here: http://amix.dk/blog/post/19588