If I were a peer reviewing this piece of work I would ask the “researcher”, “Please repeat after me, ‘correlation is not causation’. Again, ‘correlation is not causation’. Good, keep doing that until you can remember it when you are writing your papers.”

It looks to me like this guy has staked his career on something and is looking for evidence to support his hypothesis. And of course if that is all you are looking for and you ignore contradictory evidence you can probably convince yourself your hypothesis is valid.

Here is a sample of his conclusions:

Straus analyzed the results of four studies and found that spanking and other corporal punishment by parents is associated with an increased probability of three sexual problems as a teen or adult:
• Verbally and physically coercing a dating partner to have sex.
• Risky sex such as premarital sex without a condom.
• Masochistic sex such as being aroused by being spanked when having sex.

“These results, together with the results of more than 100 other studies, suggest that spanking is one of the roots of relationship violence and mental health problems. Because there is 93 percent agreement between studies that investigated harmful side effects of spanking, and because over 90 percent of U.S. parents spank toddlers, the potential benefits for prevention of sexual and relationship violence is large,” Straus says.

I haven’t read all his papers so it’s possible he has considered an alternate hypothesis but I could find no evidence of that in the web pages I viewed this morning. The alternate hypothesis that is just “screaming at me” is that children with behavioral problems are more likely to behavioral problems as adults. And if they have more behavioral problems as children then they are more likely to get spanked.