Any states that allow this are really seeing pretty much the last generation of people who will face execution. The deaths of Cruz and Roberson were only the third multiple executions in Texas since 1982, when capital punishment resumed in the state. The case of Oliver David Cruz has ignited a controversy over who is considered mentally retarded in the eyes of the law, and just how justice is administered to the mentally retarded who are on death row. Of the 3,600 Americans sentenced to death, experts estimate that about 10 percent of them are considered mentally retarded, a figure that does not correlate with the population at large. One measure usually used is how well the person adapts to changes in situations, which is a judgment call for any psychologist.
Many psychologists say IQ tests are a very limited way to measure a person's mental capacity.
They say different IQ tests can yield different results. Some say the measure should not be IQ, but the ability to distinguish right from wrong. But psychologists say the mentally retarded may not understand right from wrong the way other people do and sometimes confess to crimes because they are too anxious to please authorities. That doesn't mean you don't punish them. You send them to prison and you don't let them out to protect society.