A large study of Finnish men found that lower IQ scores were associated with committing more crimes and engaging in a wider variety of criminal offenses.
Men with the lowest IQ were the most likely to have criminal records, especially for violent crimes.
However, the increase in criminal behavior was gradual as IQ decreased, rather than occurring only below a certain IQ threshold.
The research adds to extensive evidence tying lower cognitive ability to antisocial behaviors.
Key Facts:
- Men with lower IQ scores had more criminal convictions from ages 15-21, based on records.
- The association between IQ and crime was mostly linear, with offending steadily increasing as IQ decreased.
- Men with IQ scores of 1-3 were 3.6x more likely to have a felony conviction by age 21 compared to men scoring 7-9.
- Verbal, mathematical, spatial reasoning and overall IQ composite scores all showed similar patterns.
- There was a slight uptick in offending for men with the very lowest IQ scores compared to the next lowest group.
Source: Intelligence
Lower Intelligence Linked to More Diverse Criminal Activity
A research team led by Joseph A. Schwartz analyzed IQ and criminal records in a group of 21,513 Finnish men.
They examined data on the men from birth up to age 21, from 1987 to 2008.
The goal was to clarify the relationship between intelligence, as measured by IQ scores, and criminal offending.
The researchers looked at IQ in a few ways.
They used scores on verbal reasoning, mathematical reasoning and spatial reasoning tests given to the men during military service around age 18-19.
They also calculated a composite IQ score.
For criminal behavior, they used a national database of convictions in Finland. This included sanctions like fines and felony convictions.
Overall, lower IQ scores were tied to having more criminal sanctions, more serious offenses like felonies, and committing a wider variety of different crimes.
For example, men with IQ scores of just 1-3 were 3.6 times more likely to have a felony conviction by age 21 compared to men with scores of 7-9.
This pattern was remarkably consistent across the different types of IQ tests and measures of criminal behavior.
Mostly Linear Increase in Offending With Lower IQ
A key question was whether crime increased gradually as IQ decreased, or only once IQ fell below a certain level.
Overall, the results showed a mostly linear pattern – offending steadily increased along with decreasing IQ.
So men with an IQ of 2 committed more crimes than men with an IQ of 3, who in turn committed more crimes than men with an IQ of 4, and so on.
There were a couple small deviations from perfect linearity.
Men with the lowest possible IQ score of 1 did not have the very highest crime rates. Rather, crime peaked one level up at an IQ of 2 before declining again.
A similar uptick occurred at the highest IQ level of 9 compared to the second-highest level of 8.
However, the researchers noted these differences were quite small.
Possible Explanations for Links Between IQ and Crime
These findings are consistent with a large body of research tying lower IQ to antisocial behaviors like crime and delinquency.
However, the reasons behind this association are still being investigated.
One possibility is that a core mental capacity called executive function, which is closely linked to IQ, may play a key role.
Executive functions like inhibition, attention control and planning are needed to consider the moral implications and consequences of behavior.
People with poorer executive function may act more impulsively and aggressively.
Related to this, lower IQ individuals may be less able to envision the future benefits of socially appropriate behavior.
They may focus more on immediate rewards.
People with higher IQ tend to score higher on traits like conscientiousness and dependability, which inhibit rule-breaking.
Lower IQ is also associated with disadvantages like worse academic performance, fewer job prospects and lower income.
This may promote criminal behavior through frustration and lack of opportunities.
However, the study authors note that low IQ alone does not necessarily lead to crime.
Social and environmental factors likely also play a crucial part.
Insights Into Theories About IQ and Crime
The research has implications for theories that try to explain links between IQ and crime.
Some views predict associations only below a certain IQ level, such as 70.
But the Finnish data showed high functioning men with IQs of 80 or above still had elevated crime rates.
This suggests IQ and crime associations persist across the full range of intelligence.
Other perspectives expect a U-shaped pattern, with extreme high and low IQ linked to more offenses.
But the findings weakly supported a linear pattern instead.
One theory proposes offenders have verbal deficits but average nonverbal skills.
Yet verbal and nonverbal IQ showed very similar relationships with criminal behavior in this cohort.
Overall, the study authors conclude that general mental ability, not just specific facets like verbal IQ, is tied to real-world antisocial outcomes.
The findings underline that researchers should account for linear effects of IQ on criminal tendencies, rather than just looking for thresholds.
However, they note that IQ is not destiny – social factors also contribute to criminal behaviors.
Limitations and Future Research: Crime & Intelligence Links
Like any study, this one has limitations that should be addressed by future work.
First, the study population included only Finnish men.
Replicating the research in more diverse populations would strengthen the conclusions.
Second, the study relied entirely on official conviction records.
These miss crimes that go undetected, which could introduce bias if lower IQ men get caught more often.
However, past research found this is not a major issue.
Finally, the causes underlying IQ-crime links remain unclear.
More work is needed on how genetic and environmental factors might interact to influence both intelligence and antisocial behavior over the life course.
In summary, this research reinforces the robust association between IQ and criminal offending, while providing insights into the nature of the relationship.
Understanding connections between cognitive capacities and real-world behaviors can potentially inform policies to support at-risk populations.
However, care should be taken not to overstate conclusions – intelligence is not destiny, and multiple factors beyond IQ drive an individual’s likelihood of engaging in crime.
References
- Study: Intelligence and criminal behavior in a total birth cohort
- Authors: Joseph A. Schwartz et al. (2015)
