Some human behaviors attract more attention than others. Homicides are rare, but very salient human behaviors. Governments investigate and keep records of homicides and social scientists have developed theories of homicides.

In the 1960s, social scientists suggested that inequality can lead to more violence. One simple reason is that the rewards for poor people to commit violent crimes increase with greater inequality in wealth (Becker, 1968).

Cross-national studies confirm that societies with more income inequality have higher homicide rates (Avison & Loring, 1986; Blau & Blau, 1982; Chamlin & Cochran, 2006; Corcoran & Stark, 2020; Fajnzylber, Lederman & Loayza, 2002; Krahn et al., 1986; Pratt & Godsey, 2003; Pridemore, 2008).

A recent article in Psychological Science replicated this finding (Clark, Winegard, Beardslee, Baumeister, & Shariff, 2020). However, the main focus of the article was on personality attributes as a predictor of violence. The authors main claim was that religious people are less likely to commit crimes and that among non-religious individuals those with lower intelligence would be more likely to commit homicides.

A fundamental problem with this article is that the authors relied on an article by a known White-supremacist, Richard Lynn, to measure national differences in intelligence (Lynn & Meisenberg, 2010). This article with the title “National IQs calculated and validated for 108 nations” claims that the values used by Clark et al. (2020) do reflect actual differences in intelligence. The problem is that the article contains no evidence to support this claim. In fact, the authors reveal their racist ideology when they claim that a correlation between their scores and skin color of r = -.9 validates their measure as a measure of intelligence. This is not how scientific validation works. This is how racists abuse science to justify their racist ideology.

The article also makes a common mistake to impose a preferred causal interpretation on a correlation. Lynn and Meisenberg (2010) find that their scores correlate nearly perfectly with educational attainment. They interpret this as evidence that intelligence causes educational attainment and totally ignore the plausible alternative explanation that education influences performance on logical problems. This has important implications for Clark et al.’s (2020) article because the authors buy into Lynn and Meisenberg’s racist interpretation of the correlation between performance on logic problems and educational attainment. An alternative interpretation of their finding would be that religion interacts with education. In nations with low levels of formal education, religion provides a moral code that prevents homicides. In countries with more education, other forms of ethics can take the place of religion. High levels of homicides would be observed in countries where neither religion nor education teach a moral code.

Aside from this fundamental flaw in Clark et al.’s (2020) article, closer inspection of their data shows that they overlooked confounding factors and that their critical interaction is no longer significant when these factors are included in the regression model. In fact, financial and racial inequality are much better predictors of national differences in violence than religion and the questionable measure of intelligence. Below I present the statistical results that support this conclusion that invalidate Clark et al’s (2020) racist conclusions.

Statistical Analysis

Distribution Problems

Not long ago, religion was a part of life in most countries. Only over the past century, some countries became more secular. Even today, most countries are very religious. Figure 1 shows the distribution of religiosity based on the Relig_ARDA variable in Clark et al.’s dataset. This skewed distribution can create problems when a variable is used in a regression model, especially if the variable is multiplied with another variable to test interaction effects.

It is common practice to transform variables to create a more desirable distribution for the purpose of statistical analysis. To do so, I reversed the item to measure atheism and then log-transformed the variable. To include countries that scored 100% on religiosity, I added 0.001 to all atheism scores before I carried out the log transformation. The distribution of log-atheism is less skewed.

The distribution of homicides (rates per 100,000 inhabitants) is also skewed.

Because homicide rates are right-skewed, a direct log-transformation can be applied to get a more desirable distribution. To include nations with a value of 1, I added a value of 1 before the log-transformation. The resulting distribution for log-homicides is more desirable.

The controversial IQ variable did not require a transformation.

Bivariate Relationships

The next figure shows a plot of homicides as a function of the questionable intelligence (QIM). There is a visible negative correlation. However, the plot also highlights countries in Latin America and the United States. These countries have in common that they were established by decimating the indigenous population and bringing slaves from Africa to work for the European colonialists. It is notable that nations with a history of slavery have higher homicide rates than other nations. Thus, aside from economic inequality, racial inequality may be another factor that contributes to violence even though slavery ended over 100 years ago, while racial inequality persists until today. Former slave countries also tend to score lower on the QIM measure. Thus, slavery may partially account for the correlation between QIM and homicide rates.

The next plot shows homicide rates as a function of atheism. A value of 0 would mean the country it totally atheistic, while more negative values show increasing levels of religion. There is no strong relationship between religion and homicide rates. This replicates the results in the original article by Clark et al. Remember that their key finding was a interaction between QIM and religion. However, the plot also shows a clear distinction between less religious countries. Former slave countries are low in religion and have high homicide rates, while other countries (mainly in Europe) are low in religion and have low homicide rates.

Regression Models

To examine the unique contribution of different variables to the prediction of homicide rates, I conducted several regression analyses. I started with the QIM x religion interaction to see whether the interaction is robust to transformations of the predictor variables. The results clearly show the interaction and main effects for QIM and religion (t-values > 2 are significant at p < .05).

Next I added slavery as a predictor variable.

The interaction is no longer significant. This shows that the interaction emerged because former slave countries tend to score low on QIM and religion.

I then added the GINI coefficient, the most widely used measure of income inequality, to the model. Income inequality was an additional predictor. The QIM x religion interaction remained non-significant.

I then added GDP to the model. Countries wealth is strongly related to many positive indicators. Given the skewed distribution, I used log-GDP as a predictor, which is also the most common way economists use GDP.

GDP is another significant predictor, while the QIM x religion interaction remains non-significant. Meanwhile, the strong relationship between QIM and homicide rates has decreased from b = -.71 without controls to b = -.25 with controls. However, it is still significant. As noted earlier, QIM may reflect education and Clark et al. (2020) included a measure of educational attainment in their dataset. It correlates r = .68 with QIM. I therefore substituted QIM with education.

However, education did not predict homicide rates. Thus, QIM scores capture something about nations that the education measure does not capture.

We can compare the social justice variables (slavery, GDP, GINI) with the personal-attribute (atheist, QIM) variables. A model with the social justice variables explains 62% of the variation in homicide rates across nations.

The personal-attribute model explains only 40% of the variance.

As these predictors overlap, the personal-attributes add only 3% additional variance to the variance that is explained by slavery, income inequality, and wealth.

Replicating Slavery’s Effect in the United States

The United States provide another opportunity to test the hypothesis that a legacy of slavery and racial inequality is associated with higher levels of homicides. I downloaded statistics about homicides (homicide stats). In addition, I used a measure of urbanization to predict homicides (urbanization). I also added a measure of income inequality (GINI). I classified states that fought for the confederacy as slave states (civil war facts). Results were similar for different years in which homicide rates were available from 1996 to 2018. So, I used the latest data.

In a model with all predictor variables, slavery was the only significant predictor. Income inequality showed a trend, and urbanization was not a unique predictor. When urbanization was removed from the model, the effect of income inequality was a bit stronger.

Overall, these results are consistent with the cross-national data and suggest that a history of slavery and persistent racial inequality create social conditions that lead to more violence and homicides. These results are consistent with recent concerns that systemic racism contributes to killing of civilians by civilians and police officers who historically had the role to enforce racial inequality.

Meta-Science Reflections

Clark et al.’s (2020) article is flawed in numerous ways. Ideally, the authors would have the decency to retract it. The main flaw is the use of a measure with questionable validity and to never question the validity of the measure. This flaw is not unique to this article. It is a fundamental flaw that has also led to a large literature on implicit bias based on an invalid measure. The uncritical use of measures has to stop. A science without valid measures is not a science and statistical results that are obtained with invalid measures are not scientific results.

A second flaw of the article is that psychologists are trained to conduct randomized laboratory experiments. Random assignment makes it easy to interpret statistically significant results. Unless something went really wrong or sampling error produced a false result, a statistically significant result means that the experimental manipulation influenced the dependent variable. Causality is built into the design. However, things are very different when we look at naturally occurring covariation because everything is correlated with everything. Observed relationships may not be causal and they can be produced by variables that were not measured. The only way to deal with this uncertainty is to carefully test competing theories. It is also necessary to be careful in the interpretation of results. Clark et al. (2020) failed to do so and make overly strong statements based on their correlational findings.

“Many scholars have argued that religion reduces violent behavior within human social groups. Here, we tested whether intelligence moderates this relationship. We hypothesized that religion would have greater utility for regulating violent behavior among societies with relatively lower average IQs than among societies with relatively more cognitively gifted citizens. Two studies supported this hypothesis”

This statement would be fine if they had conducted an experiment, but of course, it is impossible to conduct an experiment to examine this question. This also means it is no longer possible to use evidence as support for a hypothesis. Correlational evidence simply cannot verify a hypothesis. It can only falsify wrong theories. Clark et al. (2020) failed to acknowledge competing theories of homicides and to test their theory against competing theories.

The last meta-scientific observation is that all conclusions in science rests on a combination of data and assumptions. When the same data lead to different conclusions, like they did here, we get insights into researchers’ assumptions. Clark et al.’s (2020) assumptions were (a) there are notable difference in intelligence between nations, (b) these differences are measured with high validity by Lynn and Weisenberg’s (2010) questionable IQ scores, and homicides are caused by internal dispositions like being an atheist with low intelligence. Given Lynn and Weisenberg’s finding that their questionable measure correlates highly with skin tone, they also implicitly share the racist assumption that dark skinned people are more violent because they are less intelligent. The present blog post shows that an entirely different story fits the data. Homicides are caused by injustice such as unfair distributions of wealth and discrimination and prejudice based on skin color. I am not saying that my interpretation of the data is correct because I am aware that alternative explanations are possible. However, I rather have a liberal/egalitarian bias than a racist bias.