Ask HN: How to infer website quality from HN data?

When you look at points, a site with 20k points and 0 flagkilled stories vs. a site with the same points and 30% flagkilled are going to be very different. I would say flagkills are your best indicator.

Another option would be to check how many different people are posting links to a site. Each person could be given a quality rating based on how many points they have and how many other sites they post from.

Someone who posts only the same site and has low points (and low comments) is probably just the site's owner, for example.

Length of time on the front page, that filters out the sites that manipulate a front page presence their content can't sustain.