Interrogations-and-Confessions-Handbook

The Psychological Assessment 323
administration, for example, an IQ of 69, is not a ‘true’ score as a certain margin
of error would be expected due to the imperfection of the test. By a ‘true’
score we mean the average IQ score obtained from several administrations
of the test. Therefore, if the person was tested on several separate occasions,
several months apart with practice effect controlled for, the IQ scores could
easily vary by a few points. The average ‘standard error of measurement’ of
the WAIS-III Full Scale IQ is 2.3 (Wechsler, 1997), but there is some variability
across different age bands. This means that the chances are 19 out of 20 (i.e. 95%
probability) that the ‘true’ score lies within 4.6 IQ points of the score obtained
during any one administration.
Legally, there appears to be a certain mystique associated with the scientific
concept of IQ. The ‘standard error of measurement’ indicates that the IQ
obtained during any given administration is not fixed; certain allowances must
therefore be made for inherent weaknesses in any given test. Another factor
that is often not appreciated by the courts is that IQ tests measure certain
verbal and non-verbal skills rather than some ‘fixed’ overall ability. The precise
IQ score obtained depends on the specific skills measured at a given time and
the nature of the test used. The test most commonly used is the Wechsler Adult
Intelligence Scale (WAIS-III, Wechsler, 1997). Some of the individual subtests
used may have greater relevance to legal issues in a given case than others.
For example, in cases of retracted confession it is, in my experience, often assumed
by the courts that verbal skills (e.g. vocabulary, comprehension and
reasoning) are more indicative of how able the accused was in handling police
questioning than non-verbal intellectual skills. This is probably generally true,
although I would hesitate to suggest that non-verbal skills are unimportant. In
fact, one of the non-verbal subtests of WAIS-III, Picture Arrangement, appears
to measure social awareness and participation (Schill, Kahn & Meuhleman,
1968), which could be relevant to the identification of learning disability. I have
noticed that many of the defendants who appear strikingly good in their social
functioning, even when their verbal abilities are significantly impaired,
score relatively high on the Picture Arrangement subtest. This is interesting
because it is the subtest that has the highest correlation with interrogative
suggestibility (Gudjonsson, 1990b).
Persons who are detained at a police station have four basic rights, which
need not be exercised immediately.
� They have the right to remain silent, which is a part of the police caution.
The caution must be given before the suspect is asked any questions about
the alleged offence.
� They have the right to consult a solicitor.
� They have the right to have somebody informed of their arrest and
detention.
� They have the right to consult a copy of the Codes of Practice and the
Custody Record.
After advising the detainee about these rights, the Custody Officer gives him
or her a leaflet explaining their rights.