Hamzelou, J. (2017, January 17). Real-life psychopaths actually have below-average intelligence New Scientist. https://www.newscientist.com/article/2118547-real-life-psychopaths-actually-have-below-average-intelligence/

The article about which the summary was written is also free to download:

de Ribera, O.S., Kavish, N., & Boutwell, B. (2017). On the relationship between psychopathy and general intelligence: A meta-analytic review. bioRXiv, pp 1-60.

Over recent decades, a growing body of research has accumulated concerning the relationship between indicators of general intelligence and the personality construct known as psychopathy. Both traits represent key correlates of life outcomes, predicting everything from occupational and economic success, to various indicators of prosocial behavior (including avoiding contact with the criminal justice system). The findings to date regarding the association of the two traits, however, have been somewhat inconsistent. Thus, there remains a need for a more systematic investigation of the extant empirical literature. The current study reports a meta-analysis conducted to evaluate the direction and overall effect size of the relationship between these two constructs. Our analyses revealed a small, but significant, negative effect of intelligence on psychopathy. The results and impact of possible moderating variables such as type of intelligence test used are discussed. Finally, the study limitations, and possible directions for further research on this issue are detailed prior to concluding.

Reading carefully we see the actual effect is very small, except for WAIS verbal IQ .. and is complicated: … from the Discussion …

“The results of the current meta-analysis produced a small, but significant effect size (d = -0.15) suggesting that individuals who score higher on measures of psychopathic traits tend to score lower on measures of IQ. Moderator analyses determined that the type of control group, type of IQ test, and type of data reported did moderate the effect size. For instance, the effect size is larger when psychopaths are compared to a general population sample than when they are compared to non-psychopathic offenders. However, fixed effect analyses of the age of participant and sample size did not moderate the relationship. Additionally, sensitivity analyses confirmed that although the effect size is small, it appeared to be robust.

The IQ-Psychopathy relationship varied by measure of IQ, with the WAIS verbal score exhibiting the strongest relationship (d = -1.03) in line with previous research suggesting that low verbal intelligence is particularly related to psychopathic traits (DeLisi, Vaughn, Beaver, & Wright, 2010).

It is noted that a relatively large number of studies reported non-significant effect sizes including a few in the opposite direction of the overall effect size. The results demonstrated that heterogeneity in aspects of intelligence and especially in psychopathy may play a role in dampening the effect.”