>>11976787The 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.
