In 2002, the US Supreme Court ruled that executing people with an intellectual disability was a “cruel and unusual punishment”, and therefore unconstitutional. For someone to be classed as “intellectually disabled”, they have to demonstrate “significant limitations” in their mental abilities, like problems with literacy or social skills. These problems must also be present before the age of 18. This all usually amounts to an IQ of 70 or below. What the Supreme Court didn’t specify was how a prisoner’s IQ was to be measured, and therein lies the trouble with the ruling.
There are two worrisome problems with IQ testing. The first is that there is a margin of error when testing a person’s IQ. An IQ score is not a precise measurement, but should be interpreted as lying within a range. A prisoner’s performance could vary from day to day depending on his mood or health, and could dangerously hover around the score of 70 that has been chosen as the cut-off.
The second problem is what’s known as the Flynn Effect – James R. Flynn discovered that IQ scores increased from one generation to the next in every single country for which IQ data existed over 60 years. Nobody has been able to determine why this inflation happens, but in the US, IQ scores increase by about 3 points per decade. Different IQ tests have been standard at different points in history and produce cut-off scores due to this. According to Flynn, failing to correct for the inflation enters a prisoner into a “lottery” in which his eligibility for execution is determined by whichever test he takes.
Marvin Wilson, a 54-year-old Texan, was executed by lethal injection on 7th August 2012 for a murder in 1992. His lawyers argued that in 2004, Wilson’s IQ test produced a score of 61, well below the cut-off of 70. His family argued that he always struggled with basic tasks like tying his shoes and counting money and struggled in school. State and federal courts, however, rejected the claims that Wilson was intellectually disabled. They also declared that other IQ tests showed his score to be above 70.
The Supreme Court left it up to Texas to determine whether Wilson was intellectually disabled and therefore exempt from execution. The federal court noted that when Wilson scored 61 on his IQ test, the intern who administered it failed to note Wilson’s “motivation, attentiveness or cooperativeness”. As anyone who faced execution would have a clear motive to make their score as low as possible, this lack of documentation rendered Wilson’s score of 61 untrustworthy.
There doesn’t appear to be a precedent when it comes to the role of a prisoner’s IQ in determining his execution. In August 2004, Earl Davis shot and killed a security guard who was transporting bank deposits in an armoured car. Initially, he scored 75, 76, 65 and 70 on his IQ tests, together suggesting an IQ just above the cut-off of 70. However, in April 2009, a federal court ruled that the scores should be corrected for the Flynn effect, altering his scores to 66, 73, 62 and 70. The court ordered that Davis not be executed, stating, “The defendant has met his burden of establishing his mental retardation… the cogs in the machine must come to a halt.”
Kevin Green, who murdered while robbing a grocery store in Virginia in 1998, scored 71 on an IQ test taken as a teenager. Tests taken after his conviction produced results of 55, 74 and 74. Green’s lawyers argued that the results should be corrected for the Flynn effect, making his scores 65, 73 and 68. This was rejected by the court, and Green also failed to show “significant limitations” in adaptive behaviour. He was executed by lethal injection in May 2008.
The role an IQ score can play in the fate of an inmate facing execution is obviously extremely powerful, but it is crying out for standardisation. The American Association on Intellectual and Developmental Disabilities (AAIDD) task force believes it knows the way to go: a manual on assessing intellectual disability in death penalty cases, to be published next year. "I hope it will take some of the subjectivity out of such decisions," said Edward Polloway, co-chair of a task force on the death penalty for the AAIDD.
The manual will include a section on the importance of the Flynn effect and how to correct for it, but it is unclear whether courts will get behind the manual. "Who's to say what the courts are going to do?" warns Kevin Foley, a judge in Charlotte, North Carolina, who is working on a book about intellectual disability and the death penalty. As of April 2012, there are over 3,000 inmates on Death Row in the USA. Some kind of clarity is needed. Whatever decision the courts make, they had better make it soon.