Many of the comparisons in our summary tables are based on small samples, using simple correlations, and in many cases, both independent variables and dependent measures were measured around the same time. It is possible that the association between intelligence and offending is confounded because lower IQ test scores can be a result of injury, drug or alcohol use, and other lifestyle factors related to offending, and this concern might be assuaged in studies that clearly establish temporal order by measuring IQ much earlier than offending.
There are other potential confounds. As mentioned earlier in this chapter, academic achievement may mediate the association between low IQ and offending. Low intelligence is also associated with low income, and it could be the case that it is low income, and not the child’s intellectual deficits, that is leading to violent behavior (or biasing that association in some studies). Low intelligence might also lead to poor parenting. Children and parents are likely to resemble each other to some degree due to genetic similarity in the genes that influence intelligence, so it might be the case that the child’s IQ appears to be associated with violent behavior in part because of a coincidental association with parental attentiveness, involvement, education, etc. In the following section, we will focus on studies where these methodological problems are addressed to see if there are any changes in our earlier conclusions.