Dull minds and criminal acts

I have always had a warm spot for cold Finland. The people are much friendlier than their prices, which tend to be either high or higher. The Finns have a habit of singing about their landscape whilst drinking sahti, but no one is perfect. I spent some happy midsummer days in Vaasa, near the Artic circle, the guest of Per Fortelius and family, meeting his friends, photographing the local architecture and doing some artic temperature wind-surfing.

Finland is the sort of place where they do things thoroughly, things like testing the intelligence of a total population cohort of Finnish males born in 1987 and following up the results. Gold dust.

Joseph A. Schwartz, Jukka Savolainen, Mikko Aaltonen, Marko Merikukka, Reija Paananen, Mika Gisslerd. Intelligence and criminal behavior in a total birth cohort: An examination of functional form, dimensions of intelligence, and the nature of offending. Intelligence, Vol 51, July–August 2015, Pages 109–118.

https://drive.google.com/file/d/0B3c4TxciNeJZUnVoVy1YRHlNTjA/view?usp=sharing

They found that lower levels of intelligence are associated with greater levels of offending, that the IQ-offending association is mostly linear, with some curvilinear aspects at highest and lowest levels, and that the pattern is consistent across multiple measures of intelligence and offending. In some ways this is exactly as predicted and already observed, since the available literature shows that individuals with lower IQ are more likely to engage in criminal behaviour.  Criminal offending was measured with nine different indicators from official records and intelligence was measured using three subscales (verbal, mathematical, and spatial reasoning) as well as a composite measure. The results show consistent evidence of mostly linear patterns, with some indication of curvilinear associations at the very lowest and the very highest ranges of intellectual ability.

However, the advantage of these data is that they deal with an entire birth cohort, so there are no distorting effects caused by the loss of a few miscreants who might account for lots of crimes. The population is restricted to males n = 21,513 because only males in Finland do military service and sit the intelligence tests. Offending is judged from real documentary data, not from fallible self report, even more fallible when painful memories are involved. Lastly, they have verbal, mathematic and spatial IQ measures, so can investigate whether verbal intelligence has a particular effect, as some have argued.

Here are the results, for general intelligence, and all crime:

Note that violent crime is an order of magnitude higher in the bottom 20% of the population by ability than the top 20% of population by ability. The pattern is generally a linear one. The subscales of intelligence show the same pattern, though perhaps the spatial scores show a slightly less pronounced differential effect.

 

So, why do dull minds carry out criminal acts? The main effect is driven by general intelligence, so that raises a number of possibilities, in that highly g-loaded factors such as deficits in executive functions, including inhibition, processing speed, and attention are potentially linked to criminal behaviour. People with higher levels of intelligence are more dependable ( Deary et al., 2008b) and conscientious ( Luciano, Wainwright, Wright, & Martin, 2006), suggesting that they are more likely to think about the moral consequences of their actions compared to individuals with lower levels of intelligence. People with lower intelligence have been found to act more impulsively ( de Wit et al., 2007 and Funder and Block, 1989). People with lower levels of impulse control and related constructs, such as low self-control, have also been found to be significantly more likely to engage in various forms of criminal and antisocial behavior ( Gottfredson and Hirschi, 1990,Moffitt et al., 2011 and Pratt and Cullen, 2000). While only preliminary, current research suggests that lower levels of intelligence reduces the ability to weigh the costs and benefits of individual action, resulting in a greater propensity to make impulsive decisions, which in some cases involve illegal behaviour.

It is a minor finding, but the dullest are not quite the most criminal, an honour reserved for those in the 2nd decile of ability. It may be that those in the 1st decile are slightly restricted in their behaviours by their very low ability, and may be under supervision from care givers.

Equally minor, there is a slight uptick for criminality in the most intelligent, though hardly the torrent of criminal master-minds beloved of popular entertainments.

The authors say: “low intelligence is a strong and consistent correlate of criminal offending. For example, the risk of acquiring a felony conviction by age 21 is nearly four times (3.6) higher among those in the three lowest categories (1–3) of total intelligence as compared to those scoring in the top three categories (7–9). We observed differences of similar magnitude across each indicator of criminal offending and regardless of the measure of intelligence. We found no evidence for the hypothesis that deficits in verbal intelligence are more salient to criminal offending than deficits in other dimensions of cognitive ability.”

The authors mildly point out that, strictly speaking, these results may be confined to Finland. However, an easy test comes to mind: have a look at crime statistics in your country, and work out, for example, whether the crime rate for those below the 30th percentile rank is higher than those above the 70th percentile rank, and how much higher. Or, look at the crime rate in your country for those whose ability is equivalent to Finnish 30th percentile or below, which would be Greenwich IQ of 92 or below.

For group differences within nations use Emil’s calculator on tail effects for group distributions:

http://emilkirkegaard.dk/understanding_statistics/?app=tail_effects

For example, if IQ 92 is the point below which criminality increases considerably, then 30% of the blue group are at risk, and 68% of the red group. In this way one can model what levels of crime would be expected if IQ were the main cause. A hypothesis worth testing.