Category Archives: Research

Does Spanking Cause Negative Developmental Outcomes? Yes, But Our New Research Suggests That Effects Are Probably Smaller Than What We Think.

The debate over whether it is moral to spank children is well-regarded as ‘over’ in that there is a strong consensus both publicly and scientifically that it is immoral to spank children. Spanking, defined here as hitting a child on their buttocks or extremities using an open-hand with the intention of modifying undesirable child behavior, is banned in a large number of developed countries with global movements dedicated to banning the behavior. Journalists covering the research on spanking and its effects on child development are equally strong in their conclusions with a number of publications stating that yes, “The spanking debate is over.”

What is behind this consensus view? Mountains of research across family studies, developmental psychology, and social psychology that have culminated on the following conclusions:

  1. Spanking is not associated with any positive outcome.
  2. Spanking does not correct problem behavior. In other words, spanking is not effective.
  3. Spanking is associated with only negative outcomes in children.

The most recent contribution to the spanking literature is an excellent and comprehensive meta-analysis published in 2016 by Elizabeth Gershoff from the University of Texas at Austin, and Andrew Grogan-Kaylor from the University of Michigan. Despite the consensus views regarding the negative outcomes for children as a result of spanking, their meta-analysis addresses some remaining concerns in the literature.

One primary concern addressed in the 2016 meta-analysis is ensuring that spanking (as defined above) is not confounded with harsher forms of physical punishment perpetrated against children (e.g., hitting children with objects; abusive behaviors including choking and beating, in other words, what would be considered physical abuse). This distinction is important: whereas there is a clear consensus that child physical abuse can be detrimental for child development, it is less clear – and still debated – whether controlled spanking is: (1) an effective form of positive punishment that reduces problem behavior, and (2) directly (and causally)associated with negative psychosocial outcomes throughout development and into adulthood.

The results of the Gershoff and Grogan-Kaylor (2016) meta-analysis suggest that spanking is, indeed, associated with wide-ranging negative psychological and behavioral outcomes across development. Psychosocial outcomes resulting from spanking vs. non-spanking, importantly, did not differ as a function of study design (e.g., retrospective, longitudinal), measurement (e.g., observational, child-report, parent-report), or age of children at the time of spanking (ranging from toddlerhood to adolescence). In summary, the results of Gershoff and Grogan-Kaylor align with the general consensus that spanking is consistently associated with poor developmental outcomes, appears to be largely ineffective at reducing problem behavior, and has not been shown to have any positive effects on child development. (Articles covering this paper can be found here and here.)

Although research does clearly show that spanking is associated with negative psychosocial outcomes, not all confounds have been adequately addressed. This limitation of the literature is where my coauthors Eric Connolly, Madi Sogge, Todd Shackelford, Brian Boutwell, and I decided to focus our empirical efforts. The confound we were interested in was genetic confounds. Genetic confounds in this context would reflect the idea that being spanked and the psychosocial outcomes of interests such as externalizing behavior and self-regulation, for example, covary at the genetic level; meaning that the genetic variation underlying children’s propensity to be spanked are the same, to some extent, as the genetic variation underlying their problem behaviors presumed to be an outcome of spanking.

Some research addressing these genetic confounds have been conducted with results generally supporting the notion that genetic covariation can account for a large proportion of the association between spanking and psychosocial outcomes. A study by Sara Jaffee et al. in 2004 found that genetic covariation between spanking and antisocial behavior accounted for 86% of the observed association, whereas the remainder of the effect was primarily explained by nonshared environmental covariation. Another twin study conducted by Button and colleagues in 2008 found that genetic covariation between parental punitive punishment and children’s externalizing behaviors explained between 61% and 98% of the association. (Importantly this is NOT the case for the association between physical abuse and psychosocial outcomes).

Genetically informed research is hard to come by in the spanking literature. Whereas the non-genetic literature includes a wide range of psychosocial outcomes – 17 in the Gershoff and Grogan-Kaylor (2016) meta-analysis – the available genetically-informative research on spanking includes only a limited range of outcomes, such as internalizing and externalizing problems, and antisocial or conduct behavioral problems. The purpose of our research was to use all the information available in the spanking literature to provide an up-to-date analysis of the role that genetic confounds may play in a wide range of psychosocial outcomes. Specifically, we provided probable ranges of estimates of the degree to which genetic and nonshared environmental covariation could explain the reported associations from the Gershoff and Gorgan-Kaylor meta-analysis.

We conducted two studies to address our aims. The first study reported results from the Children of the National Longitudinal Survey of Youth (CNLSY). Similar to the results of earlier studies, our analyses showed that for alcohol use, delinquency, and depression, 49%, 66%, and 80% of the association, respectively between spanking and the outcomes was accounted for by genetic covariation between the traits, with the remainder explained by non-shared environmental covariation.

Our second study took a simulation modeling approach to estimate the extent to which the association between spanking and 17 psychosocial outcomes was likely to be explained by genetic covariation and non-shared environmental covariation. For all outcomes, with the exception of physical abuse, the estimates showed that genetic covariation could potentially account for the majority of the association between spanking and the psychosocial outcome of interest. Non-shared environmental covariance accounted for a relatively small, but non-trivial amount of the association between spanking and psychosocial outcomes.

So, what do these results mean for our understanding of how spanking effects children psychologically? First, our results are consistent with the notion that it is plausible to suggest that spanking, in some cases, may exert a negative impact, and certainly not a positive impact, on psychosocial development across the life course. However, there is an important caveat to this claim: The effect sizes are likely to be much smaller than what the current literature suggests. Overall, the results of genetically informative research suggesting moderate-to-large degrees of genetic covariation between spanking and psychosocial outcomes imply that once genetic variation is considered, the environmentally-mediated (casual) effects of spanking on psychosocial outcomes will be much smaller in magnitude than what non-genetically-informed studies suggest.

That the true effects of spanking on child development are likely smaller is magnitude than what the reported literature suggests is not at all to say that the negative effects of spanking on child development are non-existent. The extant research and the data in our new study strongly suggest that non-shared environmental covariation explains a non-trivial proportion of the phenotypic effect – a finding that is, in fact, consistent with causal interpretations of the negative effects of spanking.

Although the spanking debate may be ‘over’ with regard to whether spanking negatively effects children’s development, our understanding of the effects from a genetically informative perspective is far from resolved. Our work demonstrates how little genetically informative research has actually been done on the topic, and the potential impact that genetically informative research can have on the estimates we rely on to make informed policy decisions and moral arguments. So, yes, all research points to spanking having negative effects on psychosocial outcomes, but the magnitude of the effect is likely to be much smaller thank what we currently think to be the case.

You can find the OSF project here, and the pre-print of our paper here, which is currently under review for publication.

Photo by Caleb Woods on Unsplash

How Can Evolutionary Psychology Help Explain Intimate Partner Violence?


Jaimie has been out of town for nearly a week at her annual industry conference. Despite having been together for over a year, her boyfriend, Johnathan, still feels anxious when she is away on business trips. His anxiety has deepened because Jaimie has been “too busy to talk on the phone.” When Jaimie does finally return home, Johnathan ignites an argument, accusing her of spending time with her male co-workers. The argument escalates to shouting, with Johnathan accusing her of cheating on him while away. As Jaimie continues to plead her innocence and faithfulness to Johnathan, he pins her against the wall, with his hand around her neck, as he threatens to strike her if she refuses to admit her infidelity.

At some point in their lifetime, 10 to 35 percent of people experience intimate partner violence. (The numbers vary depending on the sample studied and precise definition of “intimate partner violence.”)

Why is violence among partners so common? Social scientists have proposed several theories, which primarily fall under two umbrellas: sociological explanations, and biological and psychological explanations. (Because the existing literature primarily focuses on violence in heterosexual relationships, my discussion is limited to violence between a man and a woman.)

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This post originally appeared at Behavioral Scientist on 21 September 2017.

Are Life History Trade-Offs Based On Function? A New Study [IN BUGS] Suggests Caution of Basic Theoretical Assumption


When I get to my office in the morning, I go through my email and read my journal alerts of the newest academic papers published. I often come across papers that are interesting, but today I came across a paper that really blew me away. Why? Because it used a clever research design to yield big theoretical implications — my favorite kind of paper.

The paper, “A Weapons-Testes Trade-Off In Males Is Amplified in Female Traits,” by Christine Miller, Paul Joseph, Rebecca Kilner, and Zachary Emberts published in Proceedings B caught my attention. My lab recently published a paper on trade-offs in male ejaculate quality using a life history framework, so I was interested to see how the findings of this new paper contributed to this broader research area. The research did not disappoint. The results certainly found trade-offs between weapons and testes as the title implies, but with a significant twist, humbly reflected by the last part of the title “amplified in female traits.”

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This article was originally published on my Medium account on 1 August 2019.

Why Men Have More Sex Partners Than Women


I got to my office the other morning with the goal of organizing my last data set needed for my PhD dissertation. The study is a small survey data set of 52 heterosexual couples, mostly adults in their 20s, who reported on a variety of self-report sexuality and relationship measures — pretty standard psychological research.

My topical expertise in psychology centers primarily around human sexuality. After years of studying in this area, there are two observations about human sexuality that I have more or less taken for granted at this point:

(1) Men have more sex partners than women, on average. This means that if you approach a random man on the street and ask him how many people he’s had sex with, his answer is likely to be larger than a random woman’s answer to the same question. (I don’t recommend using this approach strategy, however.)

(2) The variance, or range, of the number of sex partners within the sexes is different, with men as a group having a greater range as compared to women as a group. This means that it is likely that the most sexually successful man you know has a much larger number of sex partners than the most sexually successful woman who you know.

After my data were organized, I ran a simple analysis comparing the mean average number of lifetime sex partners between men and women to see if these basic observations held. It was unsurprising to see that my data conformed to both points: In my sample, men had a higher mean and a larger variance compared to women in their response to the question, “How many partners have you had sexual intercourse with in your lifetime?”

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This post was originally published on my Medium account on 16 July 2019.