NCPA - National Center for Policy Analysis

Disabilities and Capital Punishment

October 28, 2003

The U.S. Supreme Court found that executing people who are mentally retarded violates the constitutional ban on cruel and unusual punishment. But deciding which murder defendants have mental retardation is a muddy business, forensic experts said at the recent annual meeting of the National Academy of Neuropsychology in Dallas.

In the 2002 Atkins vs. Virginia decision, the court stated that to be considered mentally retarded a person must have deficient intellectual functioning and significant impairment in everyday life skills, identified before age 18, and including problems processing information, communicating, thinking abstractly, reasoning and controlling impulses.

But other individuals have these limitations.

  • Impulse control can also be a problem among people with attention-deficit/hyperactivity disorder.
  • Also, compared to people impaired due to exposure to a toxic substance or who had suffered a so-called closed head injury, at least one-quarter and up to two-thirds of the 33 death penalty offenders show signs of neuropsychological impairment.
  • Yet data on 33 offenders studied indicated that perhaps only one would qualify as mentally retarded based on IQ scores alone.
  • Traditionally, people with an IQ score below 70 -- about 2.3 percent of the population -- are considered mentally retarded. But to account for measurement error, a cutoff of 70 to 75 is often used -- which includes twice as many people who could be considered retarded.
  • IQ scores are periodically "renormed," meaning that they are made harder to compensate for the steady rise in IQ scores; this influences diagnoses of mild mental retardation for several years afterward.
  • Furthermore, schools are designating far fewer students as mentally retarded, whereas diagnoses of "learning disabilities" have doubled over recent decades, and the term mental retardation is generally being replaced by developmental disabilities.

Source: Karen Patterson, "Capital cases challenge psychologists," Dallas Morning News, October 19, 2003


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