It seems that if you look at the column on the right of the page, you can see upvotes and downvotes separately for recent posts. The same [n, m] format is displayed for recent comments, but it doesn't seem to actually sync with the score displaying on the comment. This feature only seems available on the sidebar: looking at the actual comment or post doesn't give you this information.
Thanks, whoever did this!
Your math-fu is simpler than mine.
That's the condition I was aiming to describe, yes. I was looking for a formula that would pick up posts that had a large proportion of downvotes, but were popular enough to imply a well-fought argument rather than a post that was simply bad.