Meta-analyses focused specifically on spanking were conducted on a total of 111 unique effect sizes representing 160,927 children. Thirteen of 17 mean effect sizes were significantly different from zero and all indicated a link between spanking and increased risk for detrimental child outcomes.It's not hard to find studies like this. Spanking is linked to lower IQs and higher violent crime rates. Eating family dinners is linked to not doing drugs. Reading to your children is linked to better performance in school.
The most common interpretation is that "linked to" means "caused by", but it takes very little intellectual discipline to see why that wouldn't be the case.
The effects do not only go one way. Children also cause parents to act differently. I would expect violent children to get spanked more than more peaceful children. Children who like books get read to more often. Teenagers who aren't off doing drugs are more likely to spend time with their families.
These studies also don't control at all for genes. Children's environment is not the only way parents effect their children. They also pass down their genes. It's not hard to imagine how more physically aggressive parents who spank more also pass down genes for violence to their children.
I remember these alternative interpretations were obvious to me in my early 20s, before I knew anything about the attempts of behavioral genetics to account for the effect of genes. When I discovered them I felt amazed and validated. Someone else actually noticed what was so apparent to me!
