Severe mental illness comprises a much narrower standard of diagnoses than those of a mental disorder. According to the American Psychological Association, SMI includes "mental disorders that carry certain diagnoses, such as schizophrenia, bipolar disorder, and major depression; that are relatively persistent (e.g., lasting at least a year); and that result in comparatively severe impairment in major areas of functioning.”
A defendant has a severe mental illness if he or she has BOTH:
The Supreme Court has recognized that the execution of two particular less culpable categories of the population is unconstitutional:
-Atkins v. Virginia (2002): executions of defendants with intellectual disability are “cruel and unusual punishment” prohibited by the 8th Amendment.
-Roper v. Simmons (2005): executions of juveniles are “cruel and unusual punishment” prohibited by the 8th Amendment.