For 20 years, developmental psychologist Elizabeth Gershoff has been chasing a question: Does spanking actually do a child any good?

"As far [back] as we have written records, people have been hitting children," Gershoff tells me. Today, spanking — hitting a child on the buttocks with an open hand — is still incredibly common. A 2015 Pew survey found that 45 percent of parents in the United States have spanked.

Given this long history, is it possible that parents throughout millennia — many with the best of intentions — were doing the right thing?

Gershoff is now even more confident in the answer: It is a resounding "no."

In a recently published meta analysis in the Journal of Family Psychology, Gershoff and University of Michigan professor Andrew Grogan-Kaylor sift through 75 studies, for a total data pool of nearly 161,000 children, and find "no evidence that spanking is associated with improved child behavior."

What's more, the analysis finds evidence that spanking is associated with troubling outcomes — like increased aggression, increased anti-social behavior, and mental health problems later in life. The size of these negative effects are small, the study notes, and there's no proof that spanking specifically caused these behaviors later in life.

For one, researchers can't conduct spanking experiments where they randomly assign children to be hit. And it's also possible that "bad" children are just spanked more, and are also generally more aggressive and anti-social throughout their lives.

But Gershoff suspects spanking does lead to these detrimental outcomes. Or, at the very least, she makes the convincing case that spanking doesn't do any measurable good. I recently discussed this with her over the phone. Here are highlights from our conversation and follow-up emails, edited for clarity and brevity.

Brian Resnick: Why do you think so many parents spank their children? Do you think they assume it's what's best for them?

Elizabeth Gershoff: I think there are two main reasons we still do it in the modern age.

One is parents think it works. And they think it works because it gets an immediate reaction out of the child. Immediately the child cries.

The parent goes "Aha! they understood that I am mad." That’s gratifying to the parent, so the parent is rewarded by getting this reaction out of the child.

The other reason is that they were raised with spanking themselves — their parents may have spanked them, or their religion may say it is important to spank — and so they have grown up with it as an acceptable practice.

BR: Why doesn't spanking actually work as a way for parents to teach their child a lesson?

EG: It might be a mild form, but spanking is a form of violence. The violence changes the relationship. It changes the power dynamic, and makes it clear to the children that you can hit somebody if you have power.

So children learn "you can hit to get what you want," and "you can use aggression." So those kids, not surprisingly, when they're with their friends, are using aggression to do what they want.

BR: I found it interesting that in the analysis you compare the effect of spanking with the effect of more serious physical abuse on behavior later in life. You found that the effect size of spanking was .25 (a smallish effect). And the effect size of abuse was .38 (closer to a medium effect). How do you interpret that?

EG: What it suggests to us is that there is this continuum of hitting. And as a society we say, "When it's physical abuse, that is definitely bad." But what we're showing is that there's this continuum of violence against children, and spanking falls along that continuum.

If spanking works, it would be the opposite of abuse. It would be that the effect size is in a total opposite direction, but we don't see that at all.

BR: How do researchers generally study this link between spanking and child behavior? Seems like it would be difficult.

EG: We have to ask parents how often they do it. Then, you find out things about the child's behavior either through a parent report, or a teacher report, or an observation. Then you use statistics to see how related those two things are.

Other studies have looked … at changes in the child's behavior over time. [Those studies find] spanking makes kids who start out as not aggressive, aggressive, and makes the kids with aggression behave with more aggression.

BR: What do you say to the people who say this data just show correlation rather than causation?

EG: Let's say if — in the real world — spanking was good for kids, some of these studies should have found that and found an effect in the other direction. [Only one study of the 75 found an effect linking spanking to a positive outcome.]

In order for that conclusion to be right, that spanking is good for kids, we have to have some correlations in that direction, but we don't. All the correlations are in the negative direction.

BR: There are so many children who have been spanked, and a lot of them are just fine. Should every parent who has spanked their kid feel guilty? What's the takeaway?

EG: Let's be realistic, most people who were spanked were spanked as children. And as everyone likes to tell me, they turned out okay. And me included. I think I turned out okay despite being spanked.

The question is: Did other things counter balance the spanking?

I don't think we learn to be good people who care about others by being hit. … [We learn from our parents,] who talk to us about the value and the morality of sharing with other people and taking turns and thinking about others' feelings.

We know now that children need to be in car seats and seat belts. But those of us who grew up in the 1970s were in cars that didn't even have seat belts. Do I think my parents were bad parents for not putting me in a seat belt? No, because no one understood how important seat belts were to protecting children. Do I think I "turned out okay" because I wasn’t in a seat belt? No — I think I was lucky. It's the same with spanking.

We turned out okay in spite of being spanked, not because of it.

BR: If parents shouldn't spank, what should they do instead when their kids really misbehave?

EG: What's difficult is that there is no magical disciplinary method that I can say works for all kids in all situations for all ages. If the goal is to teach children to behave, the most important thing is to teach. Explain to children why their behavior is wrong and what we want them to do in the future — that's the most important part.

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