One of the challenges of a karma / rating system is that a user's high rating can come from a very few blockbuster comments / stories, or alternatively posting tons of 1-point crap. You run into this problem when trying to tell whether a potential professor candidate (or maybe even coder) is a productive and respected researcher by his/her published paper count.
So the H-index works like this. Your H-index = how many N times you have posted a comment that has at least N points. Someone whose history has 20 comments that exceed 20 points each has an H-index of 20. It provides a more solid rating of someone's sustained good contributions and a high H-index means someone's comments are both high quality and many.
(You might know this in sports too, for example biking. How many N days have you ridden longer than N miles? That's a H-index score. And it's hard to change with little blips in behavior.)
But unfortunately I'm not an adept coder myself or right now able to use the HN API to figure out how to do this. I see in the documentation that the things you would need to calculate / query this are not available (or maybe I just don't know enough about it):
-- the complete list of HN users
-- linked table from user to all the user's comments
-- score of each comment
(from here: https://github.com/HackerNews/API)
I wonder if anyone else might have an idea about how to do this, or maybe even the HN team. I'm not proposing replacing the karma system which drives the usefulness of the site and people's behavior. I'm just interested in offering a function that can show this to people!
Although can't you just, after accounting for stories posted, divide karma by number of posts and get an average? Doesn't that accomplish what you're after, ie higher average points per post implies higher quality?
And tech ppl rank everything under the sun cuz it's easy for them to build. But Good Rankings shrink the info sphere. Random rankings of randomness explode the info sphere.