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Psycholokv in
the
Schools
Volume
28.
April 1991
STABILITY OF WISC-R SCORES IN CHILDREN
WITH LEARNING DIFFICULTIES
EDWARD
BAUMAN
Lakehead
University
Student records
of
130
children with learning difficulties who had been tested twice
were examined to determine the stability
of
WISC-R scores over time. There were
significant losses in Verbal 1Q and
Full
Scale IQ. Subjects in the above-average 1Q
range had greater
losses
in Verbal IQ and Full Scale IQ and greater gains in Perform-
ance
IQ
than did those in the below-average IQ range. Children initially tested before
age
8
had
a
significant IQ
loss,
but those tested after age
8
maintained a constant
IQ. The WISC-R is
most
frequently administered to children with learning difficulties.
Results presented here suggest that the IQs in this population are not
as
stable as
was previously thought, and this may provide a rationale for the periodic readministra-
tion
of
the WISC-R.
It is generally held that WISC-R scores have a high degree of stability over time,
and that retesting produces small, predictable gains. Wechsler
(1974)
reported that
retesting on the WISC-R after a 1-month interval produced a gain of
7
IQ points on
the Full Scale IQ (FSIQ),
4
points on the Verbal IQ (VIQ), and
10
points on the Per-
formance IQ (PIQ). Sattler
(1982)
attributed these gains to a practice effect. He reported
stability coefficients
of
.90
for the Performance,
.93
for the Verbal, and
.95
for the Full
Scale scores.
A
number of studies of learning-disabled and retarded populations have given fur-
ther support to the claims
of
stability of WISC-R scores. Vance, Blixt, Ellis, and DeBell
(1981)
reported stability coefficients
of
.SO
for the VIQ,
.91
for the PIQ, and
.88
for
the FSIQ in a population
of
exceptional children tested over a 2-year interval. Their
sample scored
2
points lower on the VIQ, 2 points higher on the PIQ, and remained
unchanged on the FSIQ. Smith and Rogers
(1978)
found stability coefficients ranging
from
.79
to
.82
in a population of learning-disabled children who were retested after
a 6-month interval. Vance, Hankins, and Brown
(1987)
contributed further evidence
for the stability
of
WISC-R scores from their study of learning-disabled and mentally
handicapped children over a 6-year interval. Their coefficients ranged from
.53
to
.87
and are lower than those previously reported, but they attributed this finding to the length
of
the retest interval and still maintained that WISC-R IQ measures are stable over a
6-year period. Oakman and Wilson
(1988)
found that IQ scores in a sample
of
learning-
disabled children remained stable over a 3-year period. IQ changes of
4
points or less
were found in
52%
of their sample.
The stability
of
WISC-R subtest patterns was investigated by Smith (cited in Vance
et al.,
1987).
He found that the subtest scale score profile
was
remarkably stable over
a 7-month test-retest interval in
a
population of learning-disabled children. There was
a
slight drop in VIQ, a significant increase in PIQ, and a gain of
2.2
points in FSIQ.
The research on the stability of IQ scores is pertinent to the controversy over the
need for a reassessment of exceptional children in special education programs every
3
years, as is mandated by Public Law
94-142.
There are some who regard the practice
as unnecessary (Oakman
&
Wilson,
1988),
expensive (Smith,
1982),
and of little value
Requests for reprints should be sent
to
Edward Bauman, Dept. of Psychology, Lakehead University,
Thunder Bay, Ontario, Canada P7B
5E1.
95