adding precise numbers
That's not necessarily what I mean by a "well-specified forecast". Be careful not to confuse "precise" and "accurate"... For instance by "downvoted" do you mean "net votes below 0", "having received any downvotes", or "net votes at -4 or below"?
The last - by "downvoted threads" I meant "threads descended from a comment at -4 or less" (though there should also be an effect for threads whose most downvoted parent is at -3 or at -2). It's a bit of a pity there isn't a standard name for those.
I just found out that a new website feature was implemented 2 days ago. If a comment is voted to -4 or below, it and all replies and downstream comments from it will be hidden from Recent Comments, and further replies in that subthread will incur 5 karma points penalty. The hiding, but not karma penalty, applies retroactively to comments in that subthread posted before the -4 vote.
This seems to be worth a discussion post since most people are probably still voting things to below -3 without knowing the new consequences of doing so.