Mental Retardation and the Death Penalty

The execution of mentally retarded prisoners has been a controversial topic for decades. The U.S. Supreme Court has found, in Atkins v. Virginia (2002), that such executions are unconstitutional; this decision was partially based on the community’s evolving standards of decency. The legal system requires mental health professionals to determine whether a prisoner is mentally retarded, which is a difficult and controversial task.

In 1989, the Supreme Court in Penry v. Lynaugh had determined that the mentally retarded, as a class, should not be protected from receiving the death penalty. Instead, defendants’ mental status should be considered on a case-by-case basis, with individual factors determining whether each defendant is eligible for the death penalty. The Court found that individuals with mental retardation vary greatly in their capacity and culpability; thus, a blanket exclusion was not appropriate. After the Penry decision, many states enacted new statutes or adapted their existing death penalty statutes to exempt the mentally retarded.

In 2002, the Supreme Court reversed itself in Atkins v. Virginia. The Court determined that the execution of mentally retarded prisoners was a violation of the Eighth Amendment’s prohibition of cruel and unusual punishment. They relied heavily on evidence that the majority of states’ statutes forbid the execution of the mentally retarded. Even those states that still permitted such executions had not carried out an execution of a mentally retarded prisoner in the preceding years.

In addition, the Atkins court found it significant that the execution of the mentally retarded was opposed by professional organizations, including the American Psychological Association and the American Association on Mental Retardation (AAMR). The AAMR’s amicus brief presented the results of 27 opinion polls; results of these polls varied but revealed that 56% to 84% of respondents indicated disfavor with the executions of the mentally retarded. No poll found more than 32% support for execution, no matter how the question was worded. This accumulation of data indicated that the execution of mentally retarded prisoners violated the community’s “evolving standards of decency” as set forth in Trop v. Dulles (1958).

Since the Atkins decision, state courts have struggled with defining mental retardation and determining what burden of proof (e.g., clear and convincing evidence) is needed to prove that a defendant is mentally retarded. Courts have also disagreed on whether the burden of proving mental retardation should fall on the defendant or the state.

Psychologists and researchers have two main roles associated with the execution of the mentally retarded. First, social science researchers have conducted public opinion polls concerning the execution of mentally retarded prisoners. Second, mental health professionals regularly conduct evaluations to determine a defendant’s level of mental retardation.

Public Opinion Research

The Atkins court found that public opinion opposed executing the mentally retarded. Psychologists confirmed this conclusion both before and after the punishment was determined to be unconstitutional. In the years after the Penry decision many polls were con-ducted, with most finding that the level of support for executing the mentally retarded was in the 20% to 30% range. More recently, surveys published in 2003 and 2004 found that the rates of support for execution of the mentally retarded were 12.5% and 29%, respectively. In general, these polls confirm the Court’s finding that such executions violate the community’s “evolving standards.”

The Role of Mental Health Professionals

The Atkins court determined that the mentally retarded suffer from cognitive, behavioral, and volitional impairments that affect their impulse control. As a result, the death penalty is less likely to be a deterrent. Furthermore, mentally retarded individuals are less culpable and thus do not deserve harsh treatment. The Court relied on clinical definitions of mental retardation when identifying three criteria that determine the existence of mental retardation: subaverage IQ, poor adaptive skills, and onset of symptoms before the age of 18.

The legal system requires mental health professionals to conduct evaluations to determine a defendant’s level of impairment and mental retardation. This is not an easy task, as mental retardation is difficult to identify. Mental health professionals generally measure IQ, processing ability, decision-making ability, impulse control, and adaptive functioning. Critics question whether such tests should be used to make life-or-death decisions because of their inherent limitations. For instance, a defendant’s score on an IQ test is considered a major factor in determining whether he is mentally retarded. However, “intelligence” is a subjective, multifaceted construct without a standard test. Instead, an examiner constructs a unique test for each defendant. Thus, two examiners would likely create two different tests that could produce two different scores. IQ tests have been criticized for many reasons, including their lack of test-retest reliability. Because mental retardation is such an elusive construct, some trials become battles of the experts to determine whether or not a person is mentally retarded.

To complicate things further, there is no uniform legal definition for mental retardation. Each state can determine its own standard, which can be a subjective endeavor. For example, states differ on the IQ score that indicates mental retardation. Some critics note that, because of varying standards, a defendant who fits the criteria for mental retardation in one state would not do so in another state.

In sum, the Supreme Court has found that the public’s standards of decency forbid the execution of mentally retarded prisoners, an assertion supported by a great deal of research. Despite the Supreme Court ruling, the assessment of the mentally retarded comes with controversy.


  1. Atkins v. Virginia, 122 S.Ct. 2242 (2002).
  2. Boots, D. P., Cochran, J. K., & Heide, K. M. (2003). Capital punishment preferences for special offender populations. Journal of Criminal Justice, 31, 553-565.
  3. Boots, D. P., Heide, K. M., & Cochran, J. K. (2004). Death penalty support for special offender populations of legally convicted murderers: Juvenile, the mentally retarded and the mentally incompetent. Behavioral Sciences and the Law, 22, 223-238.
  4. Caplan, P. J. (2004). Bias and subjectivity in diagnosing mental retardation in death penalty cases. In P. J. Caplan & L. Cosgrove (Eds.), Bias in psychiatric diagnosis (pp. 55-59). Lanham, MD: Jason Aronson.
  5. Penry v. Lynaugh, 109 S.Ct. 2934 (1989).
  6. Trop v. Dulles, 356 U.S. 86 (1958).

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