Shield Defense Rate

I've searched trhough the forums, but to no avail, so:
how is it calculated? Which stats are used regarding shield defense, etc? Anyone knows?
Same goes for perfect shield defense, too, if anyone knows how it works, sharing the knowledge would be welcome :)

I cant recall the exact formula by heart. It's affected by dex. Anyway I'd always recommend -con for dwarfs (+4 str, +4dex, +4wit).
Unless anyone enlighten, I'd look for the forumla.