Dull minds and criminal acts go together, Finnish researchers have confirmed:
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.
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.
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.