Interrogations-and-Confessions-Handbook

322 A Psychology of Interrogations and Confessions
in miscarriages of justice. Clinical impressions by mental health professionals
about the defendant’s intellectual strengths and weaknesses are often misleading.
In one case, a prison medical officer described a defendant in court as being
of ‘average intelligence’. It was only during the cross-examination of the doctor,
at my instigation, that it transpired that his conclusion was based on a clinical
impression from a very brief (5–10 minute) interview and certainly not on
actual testing. I had tested the defendant and found him to have a Full Scale IQ
of 69! This was the first case where I testified in a criminal trial in relation to a
retracted confession. It was at the beginning of 1982. In addition to a significant
intellectual impairment, I had found the defendant to have severe anxiety problems.
The judge admitted the evidence in relation to the IQ, but refused to hear
the evidence in relation to the defendant’s anxiety problems. The judge then
ruled the confession admissible and the defendant was convicted of murder.
There is evidence (Clare & Gudjonsson, 1991) that the majority of persons
with a mild learning disability do not realize that they should inform the police
of their disability if detained at a police station. Furthermore, 30% of the participants
in the study stated that they would not tell the police about their learning
disability, because they regarded the information as private and personal. This
means that many persons with learning disability may deliberately try to cover
up their deficits, including reading disability, which may inadvertently mislead
the police.
Another problem with the identification of learning disability is that professional
views on what should be the upper limit with regard to IQ vary immensely.
Denkowski and Denkowski (1985) and Richard, Spencer and Spooner
(1980) report that the cut-off scores for legal purposes range from 60 to 78. In
the WAIS-R manual a score below 70 is considered to define learning disability
(the same criterion applies to the WAIS-III). The cut-off point of 70 is quite
arbitrary and was chosen on an historical rather than scientific basis. The convention
seems to be not to unnecessarily label people, but keeping to such a low
threshold runs the risk of intellectually impaired defendants not being properly
provided with the assistance they need when interviewed by the police. There
is now a trend not to rely rigidly on fixed IQ scores, but to judge each case on
its own merit (British Psychological Society, 2001). In fact, an IQ of 75, which
represents the bottom five per cent of the adult population, would be more in
line with scientific thinking about a significant impairment and abnormality.
An IQ of 70 represents the bottom two per cent of the general population and
it is the figure that the Lord Chief Justice adopted in the case of Masih ([1986],
Crim.L.R. 395). He considered an IQ of 69 or below as a definition of learning
disability. The problems with this rigid legal definition are that no account
is taken of social functioning and the ‘standard error of measurement’ of any
given intelligence test. In certain cases, an assessment of social functioning is
undoubtedly relevant to the deliberation of the judge and jury.
The ‘standard error of measurement’ of a given test has an important legal
significance (Matarazzo, 1990), because it indicates the actual band of error
around the obtained IQ score. This band of error is associated with variations
in scores when people are tested on different occasions due to inherent
unreliability of the test itself. Therefore, a score obtained from a single test