Luke Ford

NYTIMES.com: “Mr. Hernandez’s lawyer is seeking to have the confessions thrown out, suggesting that his client, who has an I.Q. of about 70 and a history of mental illness, gave a false or coerced confession.”

If people with low IQs are more likely to commit crimes (which the evidence suggests), society needs to keep closer tabs on them.

REPORT: The majority of studies have found IQ differences between offenders and nonoffenders (e.g., Ellis & Walsh, 2003). On average, the IQ for chronic juvenile offenders is 92, about half a standard deviation below the population mean. For chronic adult offenders, however, the average IQ is 85, 1 standard deviation below the population mean. A study of Texas inmates who entered the prison system in 2002 indicated that approximately 23% of the inmates scored below 80, almost 69% scored between 80 and 109, and only 9.6% scored above 110 (Ellis & Walsh, 2003).

To give readers an understanding of the relative proportions of individuals with IQs in those ranges, we offer the following statistics, from Ellis and Walsh (2003): Only 9.18% of individuals in the general population score at or below 80, 63.39% have an IQ
between 80 and 109, and 25% have an IQ at or above 110. These data clearly show that low-IQ offenders (below 80) are substantially overrepresented in the Texas prison population (23%–9.18%), that those with scores between 80 and 109 are modestly overrepresented compared with the nonincarcerated population (69%–63%), and that individuals with IQ scores at or above 110 are underrepresented in the Texas prison
population (9.6%–25%). Data from every other state reveal the same pattern.

IQ scores derived from prison inmates depict a clear relationship between IQ and offending; however, it is important to note that some scholars question the validity of this association. They question whether criminal justice processes function so that intellectually dull offenders are more likely to be incarcerated. If so, the
association between IQ and imprisonment would be substantially inflated. Data from nonincarcerated offenders, usually matched on criminal record, cast doubt on this criticism. Studies have found that low-IQ offenders are more likely to be involved in crime over their life course, that they are more likely to be involved in chronic property crime, and that they are more likely to commit acts of violence (Ellis & Walsh, 2003).

Their overinvolvement in crime, especially crimes involving violence, account for the reasons why they are incarcerated, not their low IQ…

Although much of the research shows that there is a modest to strong relationship between intelligence and antisocial behavior, some researchers dispute the validity of this relationship. Critics argue that the empirical association between intelligence and criminal behavior may be accounted for by other factors. They highlight three general criticisms: (1) that differences in police detection ultimately account for the IQ → crime relationship; (2) that an individual’s race and/or class may account for the relationship; and (3) that the relationship is in the opposite direction, namely, that it is antisocial behavior that leads to lower intelligence. We now examine each of these arguments in greater detail.