Spanking your IQ

I read an interesting article that proposes that spanking your child lowers your childs IQ. I thought the article brought up several good points about how stress and emotional factors could affect a person's IQ, but I don't necessarily buy the fact that you hare intellectually harming your child by spanking him. The study does not seem to account for differences such as class, parents educational level, etc that also play a big part of a person's IQ. I also do not see how a spanking, done properly, causes more stress or emotional harm of any other discapline, done properly. Now I do agree, that frequent spankings, could cause damage emotionally, and in my opinion that also borders on abuse. I think it really comes down to parents needing to know how and when to discapline and when to just ignore a behavior or redirect. Read the article for yourself here