In many countries, stipulations have been made about sentencing someone to death for a crime if they prove to have such a low IQ as to be considered
mentally deficient and therefore incapable of being fully responsible for their actions.
The recent case of Teresa Lewis
who was executed in September last year, was potentially - in hindsight - a miscarriage of justice based upon established case law.
The United States Constitution's Eighth Amendment prohibits cruel and unusual punishment, and in 2002 the US Supreme Court
over the matter, eventually conceding that without
sufficient cognitive faculties, suspects were too easily victimized by the circumstances of their arrest and subsequent disposition.
The metric was accepted that an IQ of 70 represents the lower limit of people who can be sentenced to death for a capital crime.
One interesting feature of this 'policy' is the accuracy of measured IQs and how they are applied. A recent article about IQ testing in this regard
bears the thread title
"Inaccurate IQs could
be a matter of life and death
In it, a UK psychologist seems to have cast a serious doubt on the most commonly used tests to make the determination (as was done in Mrs. Lewis'
...two of the most commonly used IQ tests: the third edition of the Wechsler Adult Intelligence Scale (WAIS-III), which can be used on people aged
between 16 and 93, and the fourth edition of the Wechsler Intelligence Scale for Children (WISC-IV), suitable for children aged between 6 and 16.
In both cases, the test manuals state that you can be 95 per cent confident that a person's true IQ lies within 4 points of their test score.
How such claims could be made and accepted as definitive should require some study, but the twist in the tale shows that:
Whitaker found that for people with extremely poor WAIS-III scores, their actual IQ could be up to 16 points higher or 26 points lower than the
score achieved. In the WISC-IV test, actual IQ may be up to 25 points higher or 16 points lower than the score achieved.
The range of error was demonstrated and should now make it's way to the Justice system for review... but lacking any motive effort, I don't think it
has been, or appears to be on its way to be, considered by the courts.
Now I expected that the math behind the doctors observation would be difficult to explain.... I was wrong;
He [Whitaker] offers a simple explanation for the wide error margins in IQ readings at the low end of the scale. The statistics used to arrive at
the 95 per cent confidence level for the tests are based on the IQs of a representative sample of the population. "But by definition, most people in
the population have average IQs," says Whitaker. "This causes problems when statistics based on the performance of people with average IQs are
assumed to apply to people with low IQs."
It's a good article, worthy of attention.