In Atkins v. Virginia, the U.S. Supreme Court held that the execution of a person with intellectual disability violates the Eighth Amendment’s Cruel and Unusual Punishment Clause. After more than a decade of Atkins litigation, we perceived there to be a substantial risk that race influences intellectual disability—and consequently, life and death—determinations. Due to the difficulty of demonstrating the influence of race in a particular case, we decided to investigate its potential effects in a controlled experiment. We did so by manipulating race in three different ways and by presenting cases with both strong and ambiguous evidence of intellectual disability. We found
statistically significant race effects when we showed the face of the defendant and when the evidence of intellectual disability we provided was ambiguous. The influence of race was more pronounced when we limited our sample to white mock jurors. Even with a relatively weak manipulation, the size of the race effect is substantial. We also discovered that many participants weighed the facts of the criminal case and the consequences of their decision (death penalty eligibility), even though it was not relevant to the determination of whether the claimant was (or was not) a person with
intellectual disability. These findings shed light on why claims of intellectual disability almost never succeed before juries: death-qualified jurors may not make the diagnostic determination based on the evidence, but instead likely upon their own assessment of death-worthiness.