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Published: van Iterson, L & A.S Kaufman (2009) Intra-individual Subtest Variability on the Dutch Wechsler
Intelligence Scales for Children--Revised (WISC-RNL) for children with Learning Disabilities, Psychiatric
Disorders, and Epilepsy. Psychological Reports, 2009, 105, 995-1008.
Running head: SUBTEST VARIABILITY ON THE WISC-RNL
Intra-individual Subtest Variability on the Dutch Wechsler Intelligence Scales for Children--
Revised (WISC-RNL) for children with Learning Disabilities, Psychiatric Disorders, and
Epilepsy
Loretta van Iterson
SEIN Stichting Epilepsie Instellingen Nederland &
School De Waterlelie, Cruquius
Alan S. Kaufman
Yale University School of Medicine
Author note
Please address correspondence to Loretta van Iterson, SEIN, Stichting Epilepsie Instellingen
Nederland. Afdeling psychologie. Postbus 21 2100 AA Heemstede, The Netherlands. E-mail:
Abstract
It is common practice to look at disparities among subtest scores (“scatter”) on an intelligence
test to establish if a score is deviant. However, it remains unclear whether subtest scatter
reflects primarily normal variation within individuals or is clinically meaningful. The present
study explored this issue based on data from 467 children with developmental disabilities
tested on the Dutch WISC-RNL. Of these children, 132 had learning disabilities, 178 had
psychiatric disorders, and 157 had epilepsy. Subtest scatter was defined as scaled-score range
(highest minus lowest scaled score). When contrasted with “normal scatter,” the overall
sample revealed higher ranges on the Performance Scale and Full Scale, although effect sizes
were small. Analysis of the data for the three separate clinical samples revealed unusual
scatter only for the sample of children with psychiatric disorders. When comparing the
clinical samples, scaled-score range was larger for the sample of children with psychiatric
disorders than for those with epilepsy. Two distinct subsamples revealed elevated ranges with
moderate effect sizes: children with autistic spectrum disorders and children with left
hemisphere seizures. These results suggest that elevated subtest scaled-score range might
characterize specific clinical samples rather than denoting an overall sign of pathology.
(199 words)
Key-words: Wechsler Intelligence Scale for Children, subtest scaled-score range, scatter,
intra-individual variability, inter-subtest variability, learning disabilities; psychiatric
disorders; childhood epilepsy.
In child neuropsychology, the clinician frequently looks for strengths and weaknesses
in the cognitive profile, often operationalized as a positive or negative difference of 1 or 2
standard deviations, in order to make a diagnosis of a developmental disorder (Sattler, 2001).
This approach is based on the assumption that a child’s profile should be uniform, and that
undue inter-subtest or intra-individual variability (scatter) can be interpreted as pointing
toward a specific strength or deficit. Two common indexes of scatter are subtest scaled-score
range (the simple difference between the highest and the lowest score in a profile) and
univariate scatter (the number of subtests deviating 1 SD from an individual’s own mean).
Kaufman (1976, 1979) showed that large intra-individual variability on these indexes, far
from being unusual, was seen frequently in the standardization sample of the WISC-R. Later,
Silverstein (1987) demonstrated that the empirically-derived moments (mean and SD) from
Kaufman's data were a function of the psychometric qualities of the test and could be
estimated from the average intercorrelations among the subtests comprising the scales. Both
subtest scaled-score range and univariate scatter make use only of the extreme values in a
profile. As a more sensitive measure of intra-individual variability, the Profile Variability
Index was proposed which, like a standard deviation, uses information derived from all
subtests (Matarazzo, Daniel, Prifitera, & Herman, 1988; McLean, Reynolds, & Kaufman,
1990). Interestingly, subtest scaled-score range was shown to correlate highly with Profile
Variability Index (Matarazzo, Daniel, Prifitera, & Herman, 1988; Boone, 1993).
The question of whether elevated intra-individual variability is a sign of pathology, or
only a reflection of the psychometric properties of the test, remains unsettled. Some
researchers have provided evidence for elevated variability in pathology (Zimet, Goodman
Zimet, Farley, Shapiro Adler, & Zimmerman, 1994; Mayes, Calhoun, & Crowell, 1998;
Greenway & Milne, 1999; Ryan, Tree, Morris, & Gontkovsky, 2006), while others ardently
advocate against any use of measures based on inter-subtest variability (Watkins & Glutting,
2000; Watkins, Glutting, & Youngstrom, 2005). In the studies by Watkins and his colleagues,
inter-subtest variability did not have a significant incremental validity in predicting academic
achievement over and above Full-Scale IQ in samples of exceptional children, mainly
children with learning disabilities. The authors argue that inter-subtest variability is of no use
as a diagnostic indicator, and its use can be considered “prescientific” (Watkins, Glutting, &
Youngstrom, 2005, p.263).
In spite of this controversy, recent Wechsler test manuals have incorporated subtest
scaled-score range in the form of base rate tables (e.g. for the WISC-III, Wechsler, 1992, and
the WISC-IV, Wechsler, 2004b). For the Dutch, the adult test version includes subtest scaled-
score range (Wechsler, 2004a), while the children’s versions do not (van Haasen, de Bruyn,
Pijl, Poortinga, lutje Spelberg, Vandersteene, et al., 1986; Wechsler, 2005).
In order to be a sign of pathology, the intra-individual variability should be
significantly different in clinical samples when compared to the standardization sample.
Significant scatter should not only be interpreted as reliable scatter – that is, genuine and not
the effect of measurement error – but also as uncommon, in the sense that the magnitude of
occurrence within the normal population is small, e.g., 5% (Crawford & Allan, 1996).
Because the Wechsler scales are well-standardized and well-researched, they are used,
in the present paper, as a model to further evaluate whether intra-individual variability is a
clinically meaningful measure of pathology. This study focused on subtest scaled-score range
because it is practical and easily computed by clinicians and is included in most recent test
manuals. Furthermore, it correlates highly with Profile Variability Index. Univariate scatter,
on the other hand, was not included because its distribution is skewed, preventing
parametrical analyses. The data refer to the Dutch WISC-R (for this purpose: WISC-RNL; van
Haasen et al., 1986) and were collected up to 2007. This version was in use in the Netherlands
for a prolonged time, thus allowing the collection of larger samples. For the newer test
version, it will take some time before sufficiently large samples are accrued, but underlying
notions about subtest scatter can be understood independent of test version. The expected
mean values of subtest scaled-score range and the cut-off values for uncommonly large ranges
for the WISC-RNL were estimated according to Silverstein (1987, 1989), aided by Owen’s
(1962) range statistics. These estimates draw on the averaged intercorrelations between the
subtests, which came from the technical manual of the WISC-RNL (de Bruyn, Vandersteene, &
van Haasen, 1986, p 139; from N = 1961 children).
Based on WISC-RNL data on 467 children from three clinical samples, the aims of this
study were (1) to study whether subtest scaled-score range in children with developmental
disabilities shows differences compared to expected (normal) values; (2) to study whether
there are differences among the clinical samples, and, if so, (3) to explore whether specific
subsamples account for these differences; and (4), to report rates of individuals with
uncommonly large subtest scaled-score ranges found in clinical samples.
Methods
Participants were N = 467 children, aged six to 16 years, with FS-IQs > 75. Overall,
353 (76%) were male. The children were entitled to benefit from distinct special school
services in The Netherlands, according to national regulations (e.g., Resing, Evers, Koomen,
Pameijer, Bleichrodt, & van Boxtel, 2002). These regulations describe the criteria for
placement in different settings specialized in, respectively, (specific) learning disabilities,
childhood psychiatric disorders, or childhood epilepsy. Generally, information from four
sources is weighted by an independent committee. These sources are the family of the child,
the present school, a psychologist who did the assessment (including the intelligence testing),
and an educational, psychiatric or medical specialist. For learning disabilities, specified
criteria in terms of academic failure must be met; for psychiatric disorders, a DSM-IV diagnosis
from a psychiatrist or qualified mental health psychologist is required; for epilepsy, a
diagnosis from a neurologist is required. In all cases, the difficulties caused by the diagnosed
condition must exceed the competencies of the regular school. Normal intellectual abilities
were a further criterion for the schools of the first two samples, but not the third (epilepsy). As
indicated, in this study FS-IQ was set to be above 75 for all. Co-morbidity is a common
phenomenon in childhood developmental disabilities and the samples are diagnostically
heterogeneous; the primary diagnosis as reflected by special school placement was the
criterion for inclusion in a sample. Diagnostic group membership – type of special school –
was the independent variable in this study. Demographic data are presented in Table 1 and
data on the Wechsler scales are shown in Table 2.
The first sample consisted of N = 132 children with (specific) learning disabilities and
the second sample consisted of N= 178 children with psychiatric disorders. The latter group
included children with neurodevelopmental disorders as well as children with behavioral and
emotional disorders related to major life events (e.g. traumas). The main diagnoses of this
sample were autism spectrum disorders (ASD), conduct disorders or oppositional defiant
disorders, reactive attachment disorders, attention deficit and hyperactivity disorders, tic
disorders, and depression. The subsamples are listed in Table 1. The percentages add up to
over 100% due to psychiatric co-morbidity.
The third sample consisted of N = 157 children with seizure disorders. Mean age at
epilepsy onset was 5.6 years (ranging from the first day of life to age 15 years with SD = 3.2).
Mean duration of epilepsy was 4.0 years (SD = 3.2). Seizure type classification, side of
epilepsy onset, and information on medication and neuroimaging are presented in Table 1.
For each participant, subtest scaled-score range was calculated for five Verbal, five
Performance, and ten Full-Scale subtests. Verbal, Performance, and Full-Scale subtest scaled-
score range was the dependent variable in the study. Mean scores are given in Table 3; z-
converted means are depicted in Figure 1. Levene’s testing for homogeneity of variances
showed no significant values for ANOVA or ANCOVA. ANOVA revealed differences in mean age
(age was higher in learning disabilities compared to epilepsy) and mean P-IQ (but not V-IQ or
FS-IQ), indicating higher P-IQ in the samples of children with learning disabilities and
psychiatric disorders compared to the sample of children with epilepsy. Also, chi-square
showed that boys and girls were unevenly distributed among the samples; significant
differences were found, indicating that the rate of boys was higher in the sample with
psychiatric disorders than the sample with epilepsy. Three separate ANCOVA’s were
undertaken (for Verbal, Performance and Full-Scale subtest scaled-score range), controlling
for the pre-existing differences in P-IQ, age, and sex. With multiple, one-sided, one-sample t-
tests, the observed clinical values were compared to the estimated expected values
(Silverstein, 1987), and effect sizes were calculated accordingly (Cohen, 1988, p.45). Overall,
alpha was set at .05 and Bonferroni corrections were used to control for family-wise errors.
With chi-square, rates of children with uncommonly high subtest scaled-score range (Verbal
Scale: ≥ 8 points; Performance Scale ≥10, and Full-Scale ≥11), expected in ~5% of the
normal population (Silverstein, 1989), were compared to this value. As this value was seen as
an approximation only, alpha was set to .001. Rates of uncommonly high subtest scaled-score
range were also compared between the clinical samples.
Results
Verbal Scale.
Comparison of means. Table 3 presents the expected mean subtest scaled-score range
for the Verbal Scale (mean = 4.7, SD = 1.7) and the observed valued for the distinct samples,
together with the results of the one sample t-tests, and Figure 1 depicts the z-converted values
of subtest scaled-score range. No differences were found between the mean expected values
and the observed values of the total sample or any of the distinct clinical samples (Table 3).
No differences were found between the means of the clinical samples (ANCOVA: F(462,2) =
0.138, p = .871, n.s).
Rates of uncommonly large ranges. Large ranges (≥ 8 points) were found,
respectively, in 8.3%, 12.9% and 15.3% of the children with learning disabilities, psychiatric
disorders, and epilepsy. Compared to the expected rates, these values reached significance for
psychiatric disorders (Χ2 = 23.51, p < .001) and epilepsy (Χ2 = 34.97, p < .001). Chi-square
revealed no difference in the distributions of uncommonly large ranges between the clinical
samples. There was an almost twofold rate (likelihood ratio 1.8, 95% Confidence Interval
[CI]: 0.93 – 3.6) of children with epilepsy versus children with learning disabilities.
Performance Scale.
Comparison of means. The estimated expected mean subtest scaled-score range was
5.8 (SD = 2.4). The total sample and the children with psychiatric disorders differed from the
expected value (Table 3). Significant differences were also suggested among the clinical
samples (ANCOVA: F(461,2) = 3.024, p = .050, partial η2 = .01). However, pair-wise
comparisons between the clinical samples did not yield significant results.
Rates of uncommonly large ranges. Large ranges (≥ 10 points) were found in 7.6%,
12.9%, and 7.0% of the children with, respectively, learning disabilities, psychiatric disorders,
and epilepsy. Compared to expected values, these percentages were elevated for psychiatric
disorders only (Χ2 = 23.51, p < .001). Chi-square revealed no significantly different rates
among the samples. Likelihood ratios were 1.7 (95% CI: 0.8 – 3.5) and 1.8 (95% CI: 0.93 –
3.7) for children with psychiatric disorders versus, respectively, children with learning
disabilities and children with epilepsy.
Full Scale.
Comparison of means. The expected mean subtest scaled score range was 7.3 (SD =
2.1). Values differing significantly from expected were found for the total sample and the
sample with psychiatric disorders (Table 3). Significant differences were found between
clinical samples (ANCOVA: F(462,2) = 4.130; p = .017, partial η2 = .02); specifically, subtest
scaled-score range was higher in children with psychiatric disorders than in children with
epilepsy.
Rates of uncommonly large ranges. Larges ranges (≥ 11 points) were found,
respectively, in 6.8%, 12.9%, and 10.8 % of the children with learning disabilities, psychiatric
disorders and epilepsy. Compared to expected values, significant differences were found for
psychiatric disorders (Χ2 = 23.51, p < .001) and epilepsy (Χ2 = 11.23, p = .001). Again,
differences of the large ranges between samples showed a trend that did not reach statistical
significance. Notably, however, there was almost a twofold rate (likelihood ratio 1.9, 95% CI
0.9 - 4.0) for children with psychiatric disorders compared to children with learning
disabilities.
Subsamples.
Although it is beyond the scope of this paper to enter into detail on all subsamples,
two subsamples were identified as showing conspicuously elevated subtest scaled-score
ranges relative to expected values: (a) from the sample with psychiatric disorders, the
subsample with autistic spectrum disorders (ASD, N = 58) was identified; and (b) from the
epilepsy sample, children with left focal onset seizures (LH; N = 33) were identified. Data on
these subsamples are also included in Table 2, Table 3, and Figure 1.
Table 3 shows that the ASD sample had a significantly larger subtest scaled-score
range than the expected values on the Verbal Scale, Performance Scale and Full Scale, all
with moderate effect sizes. When the ASD sample was compared to the other children with
diagnoses of psychiatric disorders (N = 120) in the psychiatric sample, mean subtest scaled-
score range was elevated for the ASD sample on the Verbal Scale (t(94.7,1) = 2.49, p = .014,
ES = 0.5) and the Full Scale (t(176,1) = 2.44, p = .016, ES = 0.4). Uncommonly large ranges
were found for the Verbal Scale in 20.7% of these children, for the Performance Scale in
15.5%, and for the Full Scale in 17.2%. The percentages were significantly elevated when
compared to expected values for the Verbal Scale (Χ2 = 30.06, p < .001), Performance Scale
(Χ2 = 13.51, p < .001), and Full Scale (Χ2 = 18.3, p < .001). Classificatory statistics revealed
that when the ASD group was contrasted to the others children with psychiatric disorders,
uncommonly large ranges had classificatory utility for the Verbal Scale: sensitivity was 21%,
specificity was 91%, Positive Predictive Power (PPP) was 52%, Negative Predictive Power
(NPP) was 70%, and likelihood ratio was 2.26 (95% CI 1.06 - 4.81). These values indicated
that when a child with psychiatric disorders is found to have a subtest scaled-score range of 8
or more points on the Verbal Scale, it will more likely belong to the group with autistic
spectrum disorders.
Within the sample of children with psychiatric disorders, none of the other subsamples
showed elevated subtest scaled-score range consistently on all scales. However, two
subsamples of children with neurocognitive developmental disorders showed elevations on
one scale—specifically, the subsample with conduct disorders had substantial scatter on the
Performance Scale and the subsample with tic disorders had elevated scatter on the Verbal
Scale. These data merely suggest hypotheses for future study, but are not presented here
because many children had multiple diagnoses and the sample sizes were too small to permit
meaningful analyses.
Table 3 shows that mean scaled-score range was higher than expected in the sample of
children with left hemisphere seizures. Significantly elevated values were seen for the Verbal
Scale (small effect size) and the Full Scale (moderate effect size). Such elevations were not
seen in the other epilepsy subsamples; planned comparisons indicated that values were
significantly different compared to the right hemisphere seizure-group for the Verbal Scale
(t(137,1) = 2.05, p = .042, ES = 0.3). Large range was found for the Verbal Scale in 21.2% of
these LH children, for the Performance Scale in 6.1%, and for the Full Scale in 15.2%. The
percentages were significant when compared to expected values for the Verbal Scale only (Χ2
= 18.26, p < .001). Classificatory statistics revealed that when the left hemisphere seizure-
group was contrasted to the right hemisphere seizure-group, there was a clear trend to find
more children with uncommonly large ranges in the Verbal Scale in the left hemisphere
seizure-group. The valued failed to reach significance due to lack of statistical power:
sensitivity was 21%, specificity was 96%, PPP was 88%, NPP was 47%, and likelihood ratio
was 6.19 (95% CI 0.67 - 38.7).
Conclusions and Discussion
The assertion that intra-individual variability is elevated in pathology, taken for
granted by some researchers and opposed by others, was the subject of analysis in this study,
which focused on subtest scaled-score range for clinical samples of children with learning
disabilities, psychiatric disorders, and epilepsy. Analyses were conducted at three levels.
At the broadest level, 467 children from three categories of developmental disabilities
(learning disabilities, psychiatric disorders, and epilepsy) were compared to the expected
(“normal”) values. Significant elevations were found in the Performance and Full Scales –
with conspicuously small effect sizes. This finding suggested that the study was profiting
from the effects of a relatively large sample size and also that possible meaningful
information was being masked by focusing on the heterogeneous total group. At the second
level of analysis, each of the clinical samples was compared to the expected values and to
each other. The sample with psychiatric disorders showed significantly more than normal
intra-individual variability on both the Performance and Full Scales. Also, the sample with
psychiatric disorders showed more variability than the sample with epilepsy on the Full Scale.
Effect sizes were larger than for the total clinical sample, but were still small. At the third and
most specific level of analysis, two homogeneous subsamples were subjected to further
scrutiny. It appeared that the sample with ASD (within psychiatric disorders) and the sample
with focal LH seizures (within epilepsy) showed elevated scatter, compared both to the
expected values and to the other children in their respective clinical original samples. For
ASD, this was true for all three scales (moderate effect sizes). For left hemisphere epilepsy,
this was true for the Verbal Scale (small effect size) and the Full Scale (moderate effect size).
When evaluating the percents of children with uncommonly large ranges, children
with (specific) learning disabilities did not display any unusual elevations relative to groups of
normal children. However, rates were increased in children with psychiatric disorders on all
scales, specifically for the ADS subsample. Rates were also increased for the sample of
children with epilepsy on the Verbal and Full Scales, more clearly so in the subsample of LH
seizures.
The fact that the Performance Scale and not the Verbal Scale yielded the significant
differences in the primary samples of this study is consistent with a diverse body of
neuropsychological literature that has shown Wechsler’s Performance subtests to be more
sensitive to brain injury and brain dysfunction than Verbal subtests (Kaufman &
Lichtenberger, 2006, chapters 8 and 9). Nonetheless, the present study suggests that elevated
subtest scaled-score range can also be seen on the Verbal Scale in specific samples.
For children with (specific) learning disabilities, no elevations were found on any
measure. These results are in line of earlier studies (Watkins, Glutting, & Youngstrom, 2005;
Flanagan & Kaufman, 2009). For children with ASD, elevated intra-individual variability has
been reported earlier (Joseph, Tager-Flusberg, & Lord, 2002). For children with epilepsy, to
the authors’ knowledge, no such studies have been reported, but the results are in line with the
large V-IQ > P-IQ discrepancies reported for children with unilateral focal onset epilepsy (van
Iterson & Augustijn, 2006) regardless of side of seizure onset. The elevations in subtest
scaled-score range on the Verbal Scale in left hemisphere epilepsy may be the result of
plasticity in the developing brain (Vicari, Albertoni, Chilosi, Cipiriani, Coni, & Bates, 2000).
The results found for children with ASD and children with epilepsy are interesting in the light
of recent research on the commonalities underlying both conditions and the findings of high
rates of subclinical EEG abnormalities in children with ASDs even in the absence of manifest
clinical seizures (Spence & Schneider, 2009).
Effect sizes increased when the selected samples were more homogeneous, suggesting
that specific samples of children with developmental disabilities may show elevated intra-
individual variability while others may not, or may even show decreased variability. Thus,
studies of subtest scaled-score range and their interpretation should take into account type of
pathology.
Scaled-score range was not found suitable for classification purposes between the
large samples; 95% confidence intervals for likelihood ratios were non-significant, though
some trends could be found. This is not surprising as scatter is a non-specific measure which
does not provide an answer as to where the variability is coming from, or if it follows some
specific pattern.
Classificatory statistics applied on selected samples indicated that an uncommonly
large range in the Verbal Scale was more likely to belong to a child with ASD and not a child
with “another diagnosis” within psychiatric disorders. Also the data suggest that uncommonly
large variability on the Verbal Scale may be characteristic of children with left, but not right,
hemisphere onset seizures; likelihood ratio was not significant, probably due to small sample
sizes.
In line with the results of this study, and pertinent to the discussion of the
interpretability of scores beyond the summed scores of a scale (Watkins, Glutting, &
Youngstrom, 2005; Flanagan & Kaufman, 2009), it is worthy noting Saling’s (2009)
perspective. Based on the results of research within a highly specific area of research in
neuropathology – epilepsy surgery – Saling (2009), advocates against the use of scales of
summed scores in neuropsychological assessment of memory functions and argues in favor of
task specific measurement.
Intra-individual variability was studied with the WISC-RNL-version – which has now
been replaced by the WISC-IIINL, and by the WISC-IV
US/UK in English speaking countries. The
study of intra-individual variability is not confined to a specific version of the Wechsler
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yielded by different batteries as well. Flanagan and Kaufman (2009) discuss the issue of inter-
subtest variability within WISC-IV Factor Indexes. The appreciation of a true difference
between subtest scores depends on knowledge of the relationship among the measures (i.e.,
the intercorrelations of the subtests) as well as the frequency of occurrence of differences in
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Table 1
Samples and Diagnoses
Sample n % n %
Learning Disabilities 132 32.3
Psychiatric Disorders 178 38.1
Autism Spectrum Disorders 58 32.6
Conduct Disorders / Oppositional Defiant Disorders 36 20.2
Attachment Disorders 28 15.7
Attention Deficit and Hyperactivity Disorders 27 15.2
Tic Disorders 19 10.7
Depression 14 7.9
Other 66 37.1
Epilepsy 157 33.6
Seizure Type:
Focal Onset / Localisation Related Seizures 87 55.4
Left Hemisphere 33
Right Hemisphere 24
Bilateral / Multifocal 32
Generalized Seizures 32 20.4
Uncertain whether Focal or Generalized 21 13.4
Unknown 17 10.8
Anti-epileptic Drug:
0 9 5.7
1 59 37.6
>1 63 40.1
n a 26 16.6
MRI positive data 29 18.5
Total 467 100
Table 2
Mean Age, Mean WISC-RNL IQs and Sex for Three Clinical Samples and Two Subsamples
(Autism Spectrum Disorders and Left Hemisphere Onset Seizures)
age (yrs) V-IQ P-IQ FS-IQ
boys M SD M SD M SD M SD
n n % & range & range & range & range
Learning Disabilities 132 91 68.9 12.8a 1.3 93.3 10.8 97.3 12.3 94.6 10.8
7.6 to 15.6 72 to 119 68 to 125 77 to 124
Psychiatric Disorders 178 159 89.3a 10.9 2.7 93.8 11.5 95.7 13.5 93.9 10.7
6.0 to 16.7 70 to 132 61 to 130 76 to 127
Autism Spectrum Disorders 58 56 96.6 9.9 2.3 96.2 12.2 96.6 14.2 95.6 11.2
6.2 to 15.1 70 to 132 61 to 124 76 to 127
Epilepsy 157 103 65.6 9.7 2.7 95.3 12.1 91.0b 11.9 92.5 10.7
6.2 to 16.7 71 to 134 66 to 135 76 to 125
Left Hemisphere Seizures 33 26 78.8 9.5 2.5 96.6 11.1 89.1 11.7 92.3 8.7
6.3 to 16.1 71 to 120 66 to 120 78 to 108
Total 467 353 75.6 11.1 2.7 94.2 11.5 94.6 12.9 93.6 10.8
6.0 to 16.7 70 to 134 61 to 135 76 to 127 a significantly higher than sample with epilepsy b significantly lower than learning disabilities and psychiatric disorders
Fig 1
Mean z-Converted Uncorrected Subtest Scaled-score Range Values and SEM-bars for Verbal
(black), Performance (white) and Full Scales (patterned), for Three Clinical Samples and Two
Subsamples
0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1,0
Total LearningDisabilities
PsychiatricDisorders
AutismSpectrumDisorders
Epilepsy LeftHemisphere
Seizures
z-sc
ore
Verbal range
Performance range
Full Scale range
SUBTEST VARIABILITY ON THE WISC-RNL
21
Table 3
Subtest Scaled-score Range: Means, SDs, t-Values, Probabilities and Effect Sizes for Three Samples and Two Subsamples contrasted to
Expected Values.
Verbal Scale Performance Scale Full Scale
Sample n M SD ta p ES M SD ta p ES M SD ta p ES
Expected Valueb 4.7 1.7 5.8 2.1 7.3 1.9
Learning Disabilities 132 4.8 2.0 0.52 ns - 5.8 2.3 0.37 ns - 7.4 2.1 0.28 ns -
Psychiatric Disorders 178 5.0 2.0 1.84 ns - 6.5 2.6 3.77 < .001 0.3 8.1 2.2 4.83 < .001 0.4
Autism Spectrum Disorders 58 5.6 2.3 2.85 .003 0.5 6.8 2.8 2.74 .004 0.5 8.7 2.3 4.48 < .001 0.7
Epilepsy 157 5.0 2.0 1.76 ns - 6.0 2.4 1.10 ns - 7.7 2.3 1.81 ns -
Left Hemisphere Seizures 33 5.3 2.2 1.64 .050 0.4 6.5 2.4 1.63 ns - 8.4 2.0 3.00 .003 0.6
Total 467 4.9 2.0 2.45 ns - 6.1 2.4 3.28 .001 0.2 7.8 2.2 4.19 < .001 0.2a one-sample t-tests for comparisons against estimated (expected) value, one-tailed tests, d.f. = N - 1 in all cases. b estimated expected values according to Silverstein (1987)