Autism, ADHD, Conduct Disorder and violent crime

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The Stockholm Youth Cohort study examined medical and legal records on all children born in Stockholm county. This enabled them to analyze the official registries of nearly 300,000 individuals between the ages of 15 and 27. These registries record psychiatric diagnoses that are made of residents while convictions of violent crimes are listed on a different database, the Swedish National Crime Registry. Many other variables were also taken into account for this study including sex, age, the presence of other psychiatric disorders, crime history of parents, and family income, among others.

The pattern of results that they found nicely illustrate both 1) why people might think a link between autism and violence exists, and 2) why this conclusion is ultimately much more complicated. In terms of raw numbers, a total of 4.4% of individuals with autism had been convicted of a violent crime versus 2.6% of individuals without autism. Analyzing this in a more statistically comprehensive way, the authors of the study found that there continued to be about a 40% increased risk between autism and conviction for a violent crime event after mathematically accounting for things such as age, sex, and some parental factors. Furthermore, this increased risk appeared stronger among individuals who had autism but who did not meet criteria for an intellectual disability. However, when the researchers also took into account other psychiatric disorders the individuals had, in particular ADHD and Conduct Disorder, the association with autism faded away and became statistically nonsignificant. Indeed, the presence of autism among individuals diagnosed with ADHD or Conduct Disorder tended to reduce the risk of violent crime

For those unfamiliar with the diagnosis, Conduct Disorder is a psychiatric disorder that describes people who tend to frequently break rules and violate the rights of others. In many ways, it is a diagnosis that explicitly describes criminal behavior. At the risk of getting a little technical, it is a bit statistically funky to include essentially criminal behavior as an independent predictor of other criminal behavior but the fact that co-occurring ADHD also diminishes the link between autism and violence lends some additional credence that it is not autism per se that is driving the association with violent crime. About 25% of the autism group also met criteria for ADHD while only about 4% met criteria for conduct disorder.