Defining mental retardation: a matter of life or death.
Always report a 10-point confidence band around IQ and adaptive scores in death-penalty cases.
01Research in Context
What this study did
Lichten et al. (2007) wrote a theory paper about death-penalty cases.
They asked: how sure must we be that a person has intellectual disability?
The team made a new score called TQ. It mixes IQ, daily-living scores, and age.
They say courts should allow a 10-point wiggle room on any test score.
What they found
The paper does not give new data. It gives a rule.
Any IQ or adaptive score could be 10 points higher or lower.
In capital cases, that band can decide life or death.
How this fits with other research
Amore et al. (2011) extend the idea. They agree scores are shaky. They add the Flynn Effect. Old IQ tests creep up about 3 points per decade. You must subtract those points before you apply the 10-point band.
Goodey (2003) sets the stage. That paper says ID labels are not fixed facts. They are ethical choices. Lichten et al. (2007) act on that view by building the safety band.
Evenhuis (1996) and Davison (1992) show the same worry in dementia work. They set cut-off scores for the DMR questionnaire. Both teams know one number can’t tell the whole story.
Why it matters
If you testify or consult in Atkins hearings, stop treating IQ 70 as a wall. Report a range: IQ 60-70, IQ 65-75, etc. Add the Flynn correction first, then the 10-point band. Tell the court why certainty is impossible and mercy is required.
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02At a glance
03Original abstract
Because persons with mental retardation cannot be executed for murder, the diagnosis becomes a life and death matter. The American Association on Mental Retardation (now the American Association on Intellectual and Developmental Disabilities) and other associations agree that IQ alone is an insufficient criterion and adaptive functioning also needs to be considered. However, there is no satisfactory quantitative measure including both IQ and adaptive functioning. We propose a solution by defining a total quotient (TQ) scale, a composite of both IQ and standardized adaptive functioning scores. We estimate the margin of error in such scores (IQ, or adaptive functioning, or TQ) is 10 points, four times the usual one SD value given by intelligence test developers. The procedure here renders moot the distinction between convergent and divergent validity.
Intellectual and developmental disabilities, 2007 · doi:10.1352/0047-6765(2007)45[335:DMRAMO]2.0.CO;2