When Daryl Atkins was convicted of abduction and murder, the jury sentenced him to death. But Atkins was mentally retarded, with an IQ of 59, and following several appeals, in the case Atkins vs. Virginia, the US Supreme Court ruled that the execution of mentally retarded defendants was precluded by the Eighth Amendment's prohibition of cruel and unusual treatments, so sparing Atkins' life.
A consequence of the ruling is that convicted criminals may find themselves tempted to feign mental retardation. In the words of psychologist David Berry and colleagues, "...in cases of conviction for capital offences, [the diagnosis of mental retardation] may literally allow a defendant to escape death."
The trouble, according to Berry and colleagues, is that the literature on the ability to detect feigned mental retardation is sparse. Now these researchers have administered the WAIS-III intelligence test, two tests of psychiatric malingering, and three tests of cognitive malingering to 26 mentally retarded people and 26 non-retarded participants who had no more than 11 years of education.
Half the non-retarded participants were given information about mental retardation and asked to fake being retarded, with a reward of $20 if they managed to do so successfully.
Faking mental retardation wasn't difficult. According to the WAIS-III, even using special indices designed to detect deliberate poor performance, the scores of the non-retarded fakers were indistinguishable from the genuinely mentally retarded. The same was true for the tests of psychiatric malingering.
However, the three tests of cognitive malingering were moderately successful at distinguishing the fakers from the genuinely mentally retarded (although some of the genuinely retarded were also classified as fakers, showing the tests lacked specificity).
An example of a test of cognitive malingering is the 'Test of Memory Malingering'. This requires participants to view 50 pictures and then say which picture in a series of pairs was among those originally viewed. Performance is known to be relatively unaffected by a broad range of neuropsychological impairments which is what makes it a useful measure of malingering.
The researchers concluded: "At present there are almost no other published data on the characteristics of individuals attempting to feign MR, making it difficult to judge how 'realistic' the present malingerers were."
Graue, L.O., Berry, D.T.R., Clark, J.A., Sollman, M.J., Cardi, M., Hopkins, J. & Werline, D. (2007). Identification of feigned mental retardation using the new generation of malingering detection instruments: Preliminary findings. The Clinical Neuropsychologist, 21, 929-942.
Link to further information on the detection of malingering.