Is it hot or not? Ranking of user modded content.

Reddit and News.YC share a feature: hotness. Users mod up and down -- but hotness is more than total points.

How should I do it?

Positive correlation with number of votes. Negative correlation with submit time. Perhaps negative correlation with time since mean or median time of mods. Perhaps adjust for rates -- a surge implies extra hotness.

How do you make the front page efficiently? I hope not to recalculate hotness for each page view -- but a naive approach might think it necessary given the continuous time decay.

A parallel service could periodically troll through the entries from the past N days and calculate their hotness -- which serves the front page. That could be updated and chached in memory inependent of front pageview count.