People who engage in impulsive violence tend to have lower IQ scores

A recent comprehensive review of existing scientific research suggests that individuals who engage in impulsive acts of violence tend to score lower on intelligence tests compared to non-violent individuals. The findings provide evidence that lower intellectual abilities may make it harder for people to resolve conflicts peacefully, though intelligence is just one piece of a complex behavioral puzzle. The research was published in the journal Intelligence.

Scientists from various disciplines have spent decades attempting to understand the underlying factors that drive aggression and violence. While past research provides evidence that lower cognitive abilities are linked to general criminal behavior, the specific relationship between intelligence and violent acts against others has remained less clear. This gap in knowledge prompted researchers to look closer at specific types of aggression.

The researchers conducted the new review to figure out if people who commit violent acts consistently show lower intellectual abilities than those who do not. They also wanted to know if this pattern holds true for different components of intelligence, such as verbal skills and nonverbal problem solving. By clarifying this connection, the scientists hoped to gather information that could help design better rehabilitation programs.

“The main motivation for this study was the absence of a systematic analysis assessing whether violence is truly related to the intelligence quotient (IQ) or whether, on the contrary, it is an independent factor,” explained Ángel Romero-Martínez, a professor of psychobiology at the University of Valencia.

“Although prior research has linked low intelligence to general antisocial behavior, there was a significant lack of specialized systematic reviews focusing exclusively on violence against others. We aimed to resolve the debate over whether low IQ is an inherent characteristic of violent behavior (acting as a facilitator) or merely an incidental variable. By conducting this meta-analysis, we were able to demonstrate that violence—particularly reactive violence—is not independent of cognitive abilities, but is significantly influenced by them.”

To explore this topic, the scientists conducted a systematic review and meta-analysis. This type of research involves gathering all previously published studies on a specific subject and combining their data using statistical tools to find an overall trend. The research team searched three major scientific databases, including PubMed and Scopus, along with exploring reference lists to find studies that measured intelligence and assessed aggressive behavior.

Out of more than 5,000 initially identified articles, the researchers removed duplicates and screened the remaining papers for relevance. They ultimately selected 131 empirical studies that met their strict inclusion criteria. For the statistical analysis, they looked at two main sets of data to evaluate group differences and behavioral associations.

The first part of the analysis compared the intelligence scores of 1,860 violent individuals against a control group of 3,888 non-violent individuals. The second part examined the statistical correlation between intelligence and aggressive behavior across a massive pool of 33,118 participants. These aggressive behaviors included a variety of actions, ranging from general hostility and poor anger control to externalizing behaviors and physical assaults.

The intelligence quotient, commonly known as IQ, is a standardized score used to measure a person’s intellectual abilities, with an average score set at 100. In their analysis, the scientists looked at full IQ scores, as well as verbal and nonverbal scores. Verbal intelligence involves the ability to use and understand language, which is important for communication.

Nonverbal intelligence relates to visual problem solving and abstract reasoning without the use of words. The data showed that violent individuals scored significantly lower on full, verbal, and nonverbal intelligence tests compared to the non-violent control groups. This gap in intelligence scores was particularly large when the violent individuals also suffered from a diagnosed mental or personality disorder.

The findings indicate that these cognitive differences are present regardless of gender. The researchers also noted that differences in socioeconomic status did not seem to explain the gap. Many of the included studies accounted for economic and educational backgrounds, and the intelligence gap remained consistent.

“What was truly surprising was just how clear and robust the relationship turned out to be,” Romero-Martínez told PsyPost. “Beyond finding a general link, the most striking aspect was the consistent relationship across all different types of intelligence (verbal and non-verbal IQ).”

When looking at the broader pool of over 33,000 participants, the scientists found a consistent negative correlation between intelligence and violence. This means that as IQ scores decrease, the tendency to engage in violent behavior tends to increase. The correlation coefficients ranged from negative 0.09 to negative 0.20, pointing to a modest but reliable link between lower intelligence and aggressive tendencies.

The research suggests that this lower intelligence is primarily associated with reactive violence. Reactive violence is defined as an impulsive, emotional outburst of aggression in response to frustration or a perceived threat. It differs from proactive violence, which is planned, calculated, and goal oriented.

The scientists propose that lower intellectual abilities might limit an individual’s mental resources for managing stress. Without strong problem solving or verbal skills, a person may struggle to process frustration and navigate conflicts peacefully. In high stress situations, this cognitive limitation can act as a facilitator for impulsive physical or verbal aggression.

“The most important takeaway is that while our study found a correlation between lower IQ and reactive violence, having a lower IQ does not mean a person will be violent,” Romero-Martínez explained. “It is crucial to understand that intelligence is just one factor within a much more complex problem involving biological, social, and psychological variables. Rather than a direct cause, a lower IQ acts as a facilitator.”

“It may limit an individual’s cognitive resources to manage stress or solve conflicts peacefully, making them more prone to impulsive or reactive aggression. Therefore, these findings should be used not to label individuals, but to improve rehabilitation programs by tailoring them to the specific cognitive needs of each person, helping them develop better non-violent coping strategies.”

“The practical significance of these effects should not be interpreted to blame or stigmatize individuals with lower IQ scores,” Romero-Martínez continued. “Instead, the real value of these findings lies in identifying the therapeutic needs of people involved in violent acts.”

“By understanding that cognitive limitations can act as a barrier to peaceful conflict resolution, we can develop more effective intervention programs tailored to individual needs. These results suggest that rehabilitation should focus on providing specific tools and strategies that match the person’s cognitive profile, ultimately helping them to manage frustration and avoid violent behavior more successfully.”

The study does have some limitations that scientists will need to address in future research. For instance, the original studies included in the review used a wide variety of different intelligence tests, which could introduce inconsistencies into the data. Additionally, the researchers only included studies published in English or Spanish, which might restrict how well the results apply to other global populations.

Moving forward, scientists plan to explore other mental factors that might influence the relationship between intelligence and reactive violence. They aim to study how specific mental processes, such as cognitive flexibility and impulse control, play a role in aggressive outbursts.

“As we gain deeper knowledge and a more nuanced understanding of these contributors, we will be better equipped to develop effective strategies to intervene and prevent this type of behavior,” Romero-Martínez said. “We do not want our work to remain solely on a theoretical level. Our ultimate ambition is for our findings to have a real-world impact. By translating this research into practical tools and evidence-based policies, we aim to provide society with better resources to address the root causes of violence and foster safer environments for everyone.”

The study, “Analysis of the intelligence quotient and its contribution to reactive violence: A systematic review and meta-analysis,” was authored by Ángel Romero-Martínez, Carolina Sarrate-Costa, and Luis Moya-Albiol.