Clinical Psychology

retardation, or attention defict disorder could be reli-
ably classified and distinguished from their peers
based on SB-5 scores. All in all, the validity of the
SB-5 looks promising.

The Wechsler Scales

Earlier versions of the Stanford-Binet had a number
of disadvantages that led David Wechsler in 1939 to
develop the Wechsler-Bellevue Intelligence Scale.
This was a test designed for adults—one that would
offer items whose content was more appropriate for
and more motivating to adults than the school-
oriented Binet. In contrast to the Stanford-Binet,
whose items were arranged in age levels, the
Wechsler-Bellevue Intelligence Scale grouped its
items into subtests. For example, all arithmetic
items were put into one subtest and arranged in
order of increasing difficulty. In addition, there
was a Performance Scale and a Verbal Scale (con-
sisting of five and six subtests, respectively). A sepa-
rate IQ for each scale could be calculated, along
with a Full Scale IQ. The systematic inclusion of
performance items helped remedy the overemphasis
on verbal skills that limited the utility of the earlier
Stanford-Binet with special populations.
Wechsler used a deviation IQ concept. This
approach, as we have seen, assumes that intelligence
is normally distributed and compares individuals
with their age peers. In effect, it compares the per-
formance of a 15-year-old with that of other
15-year-olds. This method statistically establishes
an IQ of 100 as the mean for each age group. As
a result, an IQ of 100 means the same thing for any
person, regardless of the person’s age.

The WAIS-IV

Description. A new version of the Wechsler-
Bellevue, known as the Wechsler Adult Intelligence
Scale (WAIS), first appeared in 1955. A revised edi-
tion (WAIS-R) was published in 1981. TheWechsler
Adult Intelligence Scale Third Edition (WAIS-III),was
introduced in 1997, and the most recent version, the
WAIS-IV, was published in 2008 (Lichtenberger &
Kaufman, 2009; Wechsler, 2008).

One major change, first introduced in the

WAIS-III and continued in the WAIS-IV, is the

inclusion ofreversal itemsin several subtests. On these

subtests, all examinees begin with the same two basal

items. Depending on the level of performance on the

basal items, the preceding items are administered in

reverse sequence until a perfect score is achieved for

two consecutive items. The purpose of this change

was to determine the examinee’s ability level as

efficiently as possible without having to administer

items markedly below that ability level. Another

innovation is the WAIS-IV’s ability to provideIndex

scoresin addition to the Full Scale IQ score. By

administering 15 subtests (including the new subtests

of Visual Puzzles, Figure Weights, and Cancellation;

see below), the following four Index scores can be

calculated: Verbal Comprehension, Perceptual Rea-

soning, Working Memory, and Processing Speed.

These Index scores reflect the major ability factors

that underlie the WAIS-IV subtest scores. Thus, the

F I G U R E 7-4 David Wechsler published the Wechsler-

Bellevue Intelligence Scale in 1939. Subsequent revisions of

this test have become the most widely used techniques

to assess intellectual functioning.

Stock Montage

THE ASSESSMENT OF INTELLIGENCE 207