Essentially, it's saying that...
Corporal Punishment = Lowered IQs
That's way too simple for me, so I prefer this:
Corporal Punishment + __________ = Lowered IQs
The missing link is quite nuanced though and I should add that this was an American study, so applying it to Korean households doesn't really work as well. That missing link might be that the environment at a home where corporal punishment is taking place is not a very nurturing one. There are many more problems there other than discipline. As I said, I strongly believe that parents who resort to physically disciplining their kids totally lack the communication skills and patience to properly express themselves, so they hit. It's very human, yet overly animal-like.
We could jaw for hours about what that missing link is, but as one of my Korean friends said last night,
"Why does the result have to be lowered IQs? Koreans have the highest IQs in the world and our parents used love sticks."
Corporal Punishment = Higher IQs
Of course, this summoned my KDS and like most cases where the syndrome surfaces, it turns out that he was right. Koreans, on average, actually do have the highest IQs in the world with Kim Ung-yong leading the world with a verified IQ of 210.
Of course, we'll need to figure out that missing link again.
Corporal Punishment + __________ = Higher IQs
I'm not qualified to get into this matter except for saying that perhaps the Korean education system, with it's emphasis on math and science helps give Korean IQ test-takers an advantage. Korea students are typically not allowed to use calculators or formula sheets when doing math. They have to understand why 2+2=4, unlike their American counterparts who only need to know how to type an equation or formula into a calculator. That, and the fact that Koreans are master test-takers.
Again, I'm not the best person to be talking about corporal punishment. I'm just a guy who dribbles about Korea and expat issues. This is a bit out of my league and, honestly, my interests. All I know is that my Korean wife and I have discussed this and neither one of us are going to be heading to the love stick store in the future.