J. C. Barnes

DEMONSTRATING THE VALIDITY OF TWIN RESEARCH IN CRIMINOLOGY

In a recent article published in Criminology, Burt and Simons (2014) claimed that the statistical violations of the classical twin design render heritability studies useless. Claiming quantitative genetics is “fatally flawed” and describing the results generated from these models as “preposterous,” Burt and Simons took the unprecedented step to call for abandoning heritability studies and their constituent findings. We show that their call for an “end to heritability studies” was premature, misleading, and entirely without merit. Specifically, we trace the history of behavioral genetics and show that 1) the Burt and Simons critique dates back 40 years and has been subject to a broad array of empirical investigations, 2) the violation of assumptions in twin models does not invalidate their results, and 3) Burt and Simons created a distorted and highly misleading portrait of behavioral genetics and those who use quantitative genetic approaches. “The flaws of twin studies are not fatal, but rather seem no worse (and may be better) than the flaws of the typical causal study that relies on observational data.” (Felson, 2012: ii)

A Demonstration of the Generalizability of Twin-based Research on Antisocial Behavior

Researchers typically analyze samples of twin pairs in order to decompose trait variance into genetic and environmental components. This methodological technique, referred to as twin-based research, rests on several assumptions that must be satisfied in order to produce unbiased results. While research has analyzed the tenability of certain assumptions such as equal environments, less attention has been given to whether results gleaned from samples of twins generalize to the broader population of non-twins. The current study analyzed data drawn from the National Longitudinal Study of Adolescent Health and findings suggested twins do not systematically differ from the general population of non-twins on many measures of behavior and development. Furthermore, the effects of specific covariates on measures of antisocial behavior did not appear to differ across twin status. In sum, evidence concerning the etiology of antisocial behavior (e.g., heritability estimates) gleaned from twin-based research is likely to generalize to the non-twin population.

Self-control and health outcomes in a nationally representative sample.

OBJECTIVES To explore the link between low self-control during adolescence and health problems in early adulthood. METHODS Using data from the National Longitudinal Study of Adolescent Health, we examined the relationship between varying levels of self-control and the likelihood of being diagnosed with a variety of physical and brain-based health conditions. RESULTS Results from logistic regression analyses indicated that subjects with lower levels of self-control had significantly higher odds of being diagnosed with 9 of the 10 health outcomes. CONCLUSIONS Targeting the development of self-control in childhood and adolescence may be valuable in preventing future health problems.

Estimating the effect of gang membership on nonviolent and violent delinquency: a counterfactual analysis.

This study reconsiders the well-known link between gang membership and criminal involvement. Recently developed analytical techniques enabled the approximation of an experimental design to determine whether gang members, after being matched with similarly situated nongang members, exhibited greater involvement in nonviolent and violent delinquency. Findings indicated that while gang membership is a function of self-selection, selection effects alone do not account for the greater involvement in delinquency exhibited by gang members. After propensity score matching was employed, gang members maintained a greater involvement in both nonviolent and violent delinquency when measured cross-sectionally, but only violent delinquency when measured longitudinally. Additional analyses using inverse probability of treatment weights reaffirmed these conclusions.

Psychopathic Personality Traits, Genetic Risk, and Gene-Environment Correlations:

There is a great deal of evidence indicating that psychopathy and psychopathic traits represent some of the strongest correlates to serious violent criminal behavior. As a result, there has been a recent surge of behavioral genetic studies examining the genetic and environmental factors that may be related to the development of psychopathy. The current study extends this line of research by analyzing a sample of kinship pairs from the National Longitudinal Study of Adolescent Health to estimate the extent to which genetic factors relate to measures of psychopathic personality traits created from the five factor model. Moreover, the authors also test for a series of gene—environment correlations between genetic risk for psychopathic personality traits and measures of parental negativity. The results of the analyses revealed that genetic factors explained between .37 and .44 of the variance in measures of psychopathy. Additional statistical models indicated the presence of gene—environment correlations between parental negativity and genetic risk for psychopathic personality traits.

The effect of medical marijuana laws on crime: evidence from state panel data, 1990-2006.

Background Debate has surrounded the legalization of marijuana for medical purposes for decades. Some have argued medical marijuana legalization (MML) poses a threat to public health and safety, perhaps also affecting crime rates. In recent years, some U.S. states have legalized marijuana for medical purposes, reigniting political and public interest in the impact of marijuana legalization on a range of outcomes. Methods Relying on U.S. state panel data, we analyzed the association between state MML and state crime rates for all Part I offenses collected by the FBI. Findings Results did not indicate a crime exacerbating effect of MML on any of the Part I offenses. Alternatively, state MML may be correlated with a reduction in homicide and assault rates, net of other covariates. Conclusions These findings run counter to arguments suggesting the legalization of marijuana for medical purposes poses a danger to public health in terms of exposure to violent crime and property crimes.

The Biosocial Underpinnings to Adolescent Victimization: Results From a Longitudinal Sample of Twins

Behavioral genetic research has consistently revealed that antisocial behaviors are due partially to genetic factors and partially to environmental factors. Even in light of these findings, researchers have failed to examine the genetic and environmental contributors to adolescent victimization. The current study addressed this gap in the literature by analyzing a sample of twin pairs drawn from the National Longitudinal Study of Adolescent Health (Add Health). The results of the statistical models revealed that genetic factors explained about 40% to 45% of the variance in adolescent victimization, with the remaining variance attributable to the nonshared environment. Moreover, additional analyses revealed that 64% of the variance in repeat victimization was due to genetic factors. The implications that these findings have for victimization researchers are discussed.

Analyzing the origins of childhood externalizing behavioral problems.

Drawing on a sample of twin children from the Early Childhood Longitudinal Study, Birth Cohort (ECLS-B; Snow et al., 2009), the current study analyzed 2 of the most prominent predictors of externalizing behavioral problems (EBP) in children: (a) parental use of spankings and (b) childhood self-regulation. A variety of statistical techniques were employed, and, overall, the findings can be summarized into 2 points. First, the results show that the relationships among spanking, self-regulation, and EBP are highly nuanced in that multiple explanations for their intercorrelations appear to fit the data (e.g., bidirectional relationships and shared methods variance). Second, genetic influences accounted for variance in each variable (EBP, spankings received, self-regulation) and even explained a portion of the covariance among the different variables. Thus, research that does not consider genetic influences when analyzing these associations runs a risk of model misspecification.

Physical punishment and childhood aggression: the role of gender and gene–environment interplay

A large body of research has linked spanking with a range of adverse outcomes in children, including aggression, psychopathology, and criminal involvement. Despite evidence concerning the association of spanking with antisocial behavior, not all children who are spanked develop antisocial traits. Given the heterogeneous effects of spanking on behavior, it is possible that a third variable may condition the influence of corporal punishment on child development. We test this possibility using data drawn from a nationally representative dataset of twin siblings. Our findings suggest that genetic risk factors condition the effects of spanking on antisocial behavior. Moreover, our results provide evidence that the interaction between genetic risk factors and corporal punishment may be particularly salient for males.

Genetic Risk for Violent Behavior and Environmental Exposure to Disadvantage and Violent Crime The Case for Gene–Environment Interaction

Despite mounds of evidence to suggest that neighborhood structural factors predict violent behavior, almost no attention has been given to how these influences work synergistically (i.e., interact) with an individual’s genetic propensity toward violent behavior. Indeed, two streams of research have, heretofore, flowed independently of one another. On one hand, criminologists have underscored the importance of neighborhood context in the etiology of violence. On the other hand, behavioral geneticists have argued that individual-level genetic propensities are important for understanding violence. The current study seeks to integrate these two compatible frameworks by exploring gene–environment interactions (GxE). Two GxEs were examined and supported by the data (i.e., the National Longitudinal Study of Adolescent Health). Using a scale of genetic risk based on three dopamine genes, the analysis revealed that genetic risk had a greater influence on violent behavior when the individual was also exposed to neighborhood disadvantage or when the individual was exposed to higher violent crime rates. The relevance of these findings for criminological theorizing was considered.