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WISC-III Subtest Scatter as a Function of Highest Subtest Scaled Score

Transcript of Schinka, J. a.; Vanderploeg, R.D.; Curtiss, G. (1997) WISC-III Subtest Scatter as a Function of...

  • Psychological Assessment1997, Vol. 9, No. 2, 83-88

    Copyright 1997 by the American Psychological Association, Inc.1040-3590/97/$3.00

    WISC-III Subtest Scatter as a Function of Highest Subtest Scaled Score

    John A. Schinka and Rodney D. VanderploegJames A. Haley Veterans Affairs Medical Center,Tampa, Florida, and University of South Florida

    Glenn CurtissHenry M. Jackson Foundation and James A. Haley

    Veterans Affairs Medical Center

    The Wechsler Intelligence Scale for ChildrenIII (WISC-III) standardization data were analyzedto determine the frequency of occurrence for relative intersubtest scatter ranges. The relative scatterrange was denned as the difference between the highest and lowest subtest scaled scores based onthe value of the highest subtest scaled score. This approach to intersubtest scatter provides thegreatest precision in scatter analysis to help clinicians determine whether the amount of scatterobtained in WISC-III clinical profiles is rare enough to be considered abnormal. For ease of clinicaluse, tables are provided that report frequency of occurrence for the lowest subtest scaled score byeach level of highest subtest scaled score. Potential scatter range, rather than overall level of intelli-gence, was the primary determinant of the magnitude of scatter; the greater the possible range, thelarger the magnitude of scatter.

    Since the introduction of the Wechsler scales in 1939, theanalysis of intelligence test subtest profiles has been a subjectof substantive clinical theorizing and research interest. The po-tential importance of variability in subtest profiles was spurredinitially by several reports (e.g., Black, 1974; Doehring, Rei-tan, & Klove, 1961; Simpson & Vega, 1971) of increased subtestscatter in patients with demonstrable brain damage. Althoughnumerous studies have subsequently examined intelligence-bat-tery subtest scatter in relation to a broad variety of forms ofpsychopathology, there is little substantive evidence to supportthe diagnostic utility of specific subtest patterns. Nevertheless,highly recognized texts (e.g., Kaufman, 1990; Saltier, 1988)provide strategies for generating clinical hypotheses based onsubtest scatter for the Wechsler intelligence scales.

    As we have noted (Schinka, Vanderploeg, & Curtiss, 1994),subtest score variability, or scatter, has been assessed by meansof three measures: (a) the absolute range (the difference be-tween the highest and lowest subtest scaled scores, regardlessof the value of either score; Matarazzo, Daniel, Prifitera, &Herman, 1988; McLean, Kaufman, & Reynolds, 1989; Sil-verstein, 1987, 1989); (b) the absolute subtest scaled scorerange for different levels of IQ (Matarazzo et al., 1988); and

    John A. Schinka, Psychology Service, James A. Haley Veterans AffairsMedical Center, Tampa, Florida, and Department of Psychiatry, Univer-sity of South Florida; Rodney D. Vanderploeg, Psychology Service,James A. Haley Veterans Affairs Medical Center and Departments ofNeurology and Psychology, University of South Florida; Glenn Curtiss,Henry M. Jackson Foundation, Tampa, Florida, and Psychology Service,James A. Haley Veterans Affairs Medical Center.

    This research was supported in part by the Department of VeteransAffairs. Data reported in this article are standardization data of theWECHSLER INTELLIGENCE SCALE FOR CHILDRENTHIRDEDITION. Copyright 1990 by The Psychological Corporation. Usedby permission. All rights reserved.

    Correspondence concerning this article should be addressed to John A.Schinka, Psychology Service (116B), James A. Haley Veterans AffairsMedical Center, 13000 Bruce B. Downs Boulevard, Tampa, Florida33612. Electronic mail may be sent via Internet to [email protected].

    (c) the number of subtest scale scores differing by 3 pointsfrom the individual's mean scaled score (e.g., at various fre-quencies of occurrence; McLean et al., 1989). Studies examin-ing the relationships among these measures and demographicvariables for the revised Wechsler Adult Intelligence Scale(WA1S-R; Wechsler, 1981) have shown that the range is themost effective measure (Matarazzo et al., 1988; McLean etal., 1989). Because scatter has been shown to increase withincreasing education or IQ with administration of the WAISRto adults, tables presenting the frequencies of different scatterranges are typically broken down by levels of one of thesevariables (e.g., IQ in Tables 4-6 of Matarazzo et al., 1988,and Tables 4 and 5 in McLean et al., 1989). Matarazzo et al.(1988) suggested that the greater intersubtest scatter observedat higher IQ levels deserved further exploration, because statis-tically one would expect that widely deviate subtest scoreswould average out, resulting in an IQ near the population mean.Schinka et al. (1994), however, demonstrated that the amountof scatter in the WAIS-R normative sample is simply a func-tion of the potential range of scatter, and they provided tablesfor examining the frequency of scatter on the basis of highestsubtest scale score.

    In the manual for the latest edition of the Wechsler Intelli-gence Scale for Children (WISC-III; Wechsler, 1991), the clini-cal importance of subtest scatter is recognized by the provisionof Table B5 (p. 266), which presents the percentage of childrenin the standardization sample whose scores exhibited variousamounts of absolute scatter within Verbal, Performance, FullScale, and factor-based subtest groupings. Wechsler noted inthe manual that analyses conducted to establish whether scattervaried with age or IQ level revealed no significant findings.

    In this article we provide data on frequency of occurrencefor relative, rather than absolute, scatter ranges for the Verbal,Performance, and Full-Scale subtest groupings for the WISC-III. The relative scatter range is defined as the difference be-tween the highest and lowest subtest scaled scores based on thevalue of the highest subtest scaled score. Use of relative rangesassumes that, for example, a range of 6 may have a differentmeaning when the highest subtest scaled score is 8 than it does

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  • 84 SCHINKA. VANDERPLOEG, AND CURTISS

    Table 1Verbal Scale (5 Subtexts): Percentage of Cases by Highest Subtext Scaled Scoreat or Below the Value for the Lowest Subtest Scaled Score

    Lowestsubtestscaledscore

    16151413121110987654321

    n

    MSD%

    Highest subtest scaled

    17+

    100.098.395.482.870.754.037.423.09.22.91.10.0

    17411.32.1

    38.0

    16

    100.099.294.787.971.252.328.011.43.80.80.0

    13210.51.7

    34.3

    15

    100.099.593.581.160.740.825.412.47.54.01.00.50.0

    2019.72.0

    35.2

    14

    100.099.696.382.260.239.422.09.13.31.70.80.0

    2418.81.8

    36.8

    13

    100.097.787.972.147.930.613.26.42.61.10.80.0

    2658.41.8

    35.4

    12

    luo.o99.087.364.941.823.412.07.03.31.70.7

    2997.61.8

    36.8

    11

    100.098.982.059.435.316.58.35.42.21.1

    2786.91.7

    37.2

    score

    10

    100.094.278.859.734.519.912.44.42.2

    2265.91.8

    40.6

    9

    100.096.274.550.028.316.36.53.3

    1845.31.7

    41.7

    8

    100.091.775.245.922.0

    8.33.7

    1094.51.4

    43.4

    7

    100.082.153.630.417.9563.21.4

    54.7

    6

    100.070.647.117.6172.61.1

    55.8

    Note. M = mean lowest subtest score; SD = standard deviation of mean lowest subtest score; % =proportion of the possible scatter range accounted for by average scatter (mean scatter range/highest subtestscore). Standardization data of the WECHSLER INTELLIGENCE SCALE FOR CHILDRENTHIRDEDITION. Copyright 1990 by The Psychological Corporation. Used by permission. All rights reserved.

    Table 2Performance Scale (5 Subtesls): Percentage of Cases by Highest Subtest Scaled Scoreat or Below the Value for the Lowest Subtest Scaled Score

    Lowestsubtestscaledscore

    1615141312I I10987654321

    n

    MSD%

    Highest subtest scaled

    17+

    100.099.697.691.081.666.551.031.019.210.24.92.01.20.40.4

    2459.42.3

    49.6

    16

    100.098.396.091.377.562.442.824.912.14.62.30.60.0

    1738.92.1

    44.5

    15

    100.099.698.295.586.571.756.534.522.012.14.52.20.90.4

    2238.22.2

    45.7

    14

    100.099.297.089.877.462.642.624.515.18.74.22.31.1

    2657.82.3

    44.6

    13

    100.098.291.875.351.234.118.310.14.91.20.9

    3287.11.9

    45.1

    12

    100.099.792.384.366.248.132.818.110.84.91.4

    2876.42.1

    46.5

    11

    100.097.188.072.050.234.522.912.77.33.6

    2756.12.2

    44.4

    score

    10

    100.099.592.573.550.534.018.59.05.0

    2005.21.8

    48.3

    9

    100.099.094.982.860.640.421.215.210.1994.81.9

    47.1

    8

    100.083.654.538.218.214.555

    3.91.6

    51.1

    7

    100.092.076.068.044.032.025

    2.91.7

    58.9

    6

    100.093.373.360.033.3152.41.4

    60.0

    Note. M = mean lowest subtest score; SD = standard deviation of mean lowest subtest score; % =proportion of the possible scatter range accounted for by average scatter (mean scatter range/highest subtestscore). Standardization data of the WECHSLER INTELLIGENCE SCALE FOR CHILDRENTHIRDEDITION. Copyright 1990 by The Psychological Corporation. Used by permission. All rights reserved.

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  • WISC-IU SUBTEST SCATTER 85

    Table 3Full Scale (10 Subtests): Percentage of Cases by Highest Subtest Scaled Scoreat or Below the Value for the Lowest Subtest Scaled Score

    Lowestsubtestscaledscore

    16151413121110987654321

    n

    MSD%

    17+

    100.098.394.585.168.846.130.116.38.35.02.81.10.6

    3628.42.1

    55.3

    16

    100.098.292.879.259.342.529.014.56.83.22.30.9

    2217.72.1

    51.9

    15

    100.099.399.397.288.776.151.433.823.212.34.21.10.4

    2847.12.0

    52.5

    14

    100.099.397.386.467.042.526.916.09.55.12.7

    2946.52.0

    53.8

    Highest

    13

    100.098.193.879.556.835.712.112.75.92.8

    3225.91.9

    54.4

    subtest scaled score

    12

    100.099.697.888.273.250.733.121.310.75.1

    2725.22.0

    56.7

    11

    100.098.595.082.059.538.525.010.05.0

    2004.91.8

    55.8

    10

    100.092.686.164.843.424.615.6

    1223.71.7

    62.7

    9

    100.098.594.176.555.935.325.068

    3.11.6

    65.0

    8

    100.097.572.552.537.540

    2.41.3

    70.0

    7 6

    100.090.990.972.711

    1.50.9

    79.2

    Note. M = mean lowest subtest score; SD = standard deviation of mean lowest subtest score; % =proportion of the possible scatter range accounted for by average scatter (mean scatter range/highest subtestscore). Standardization data of the WECHSLER INTELLIGENCE SCALE FOR CHILDRENTHIRDEDITION. Copyright 1990 by The Psychological Corporation. Used by permission. All rights reserved.

    Table 4Verbal Scale (6 Subtests, Digit Span Included): Percentage of Cases by Highest SubtestScaled Score at or Below the Value for the Lowest Subtest Scaled Score

    Lowestsubtestscaledscore

    16151413121110987654321

    n

    MSD%

    Highest subtest scaled score

    17+

    100.098.189.682.071.158.340.325.110.04.72.80.90.90.0

    21110.22.4

    44.4

    16

    100.099.395.988.471.450.330.615.04.84.10.70.70.0

    1479.41.9

    41.3

    15

    100.0099.597.791.875.560.540.521.410.55.91.40.90.90.5

    2208.92.0

    40.5

    14

    100.099.091.077.255.534.517.29.05.22.81.40.3

    2908.11.9

    42.4

    13

    100.099.795.185.467.349.825.214.68.13.91.91.0

    3097.52.0

    42.5

    12

    100.099.797.183.661.136.319.611.36.12.30.6

    3116.81.8

    43.1

    11

    100.099.192.776.549.124.410.36.43.01.3

    2346.41.6

    42.1

    10

    100.099.589.671.943.226.614.15.73.1

    1925.51.7

    45.4

    9

    100.098.683.058.537.417.77.52.0

    1475.01.6

    45.0

    8

    100.096.485.757.131.013.16.0

    844.11.4

    48.7

    7

    100.090.774.448.830.2432.61.3

    63.5

    6

    100.071.442.928.672.61.3

    57.2

    Note. M = mean lowest subtest score; SD = standard deviation of mean lowest subtest score; % =proportion of the possible scatter range accounted for by average scatter (mean scatter range/highest subteslscore). Standardization data of the WECHSLER INTELLIGENCE SCALE FOR CHILDRENTHIRDEDITION. Copyright 1990 by The Psychological Corporation. Used by permission. All rights reserved.

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  • 86 SCHINKA, VANDERPLOEG, AND CURTISS

    Table 5Performance Scale (6 Subtexts, Mazes Included): Percentage of Cases by Highest SubtestScaled Score at or Below the Value for the Lowest Subtest Scaled Score

    Lowestsubtestscaledscore

    16151413121110987654321

    n

    MSD%

    Highest subtest scaled

    17+

    100.099.799.797.691.778.964.546.529.415.67.03.42.41 '0.6

    3278.62.2

    530

    16

    100.099.098.497.491.180.659.236.619.49.95.21.00.50.5

    1918.02.0

    49.9

    15

    100.099.698.496.184.169.845.731.416.37.02.71.20.4

    2587.52.9

    502

    14

    100.099.294.987.871.054.134.921.611.46.7351.6

    2557.12.2

    49 1

    13

    100.099.194.983.361.842.424.813.16.02 11.2

    3356.71.9

    484

    12

    100.099.698.692.576.558.740.622.812.56.02.5

    2815.92.0

    509

    11

    100.098.392.482.363.346.030.016.0763.8

    2375.62.1

    49 1

    score

    10

    100.097.083.458.037.324.911.86.5

    1694.81.8

    51.9

    9

    100.098.692.972.954.330.022911.4704.21.8

    537

    8

    100.095.065.050.032.527.540

    3.31.7

    58.8

    7

    100.085.070.0SOO40.0202.61.5

    636

    6

    100.072.763.636,4112.31.3

    62.1

    Note. M = mean lowest subtest score; SD = standard deviation of mean lowest subtest score; % proportion of the possible scatter range accounted for by average scatter (mean scatter range/highest subtestscore). Standardization data of the WECHSLER INTELLIGENCE SCALE FOR CHILDRENTHIRDEDITION. Copyright 1990 by The Psychological Corporation. Used by permission. All right reserved.

    when the highest subtest scaled score is 15. For ease of clinicaluse, this work reports the lowest subtest scaled score for eachlevel of highest subtest scaled score, rather than a value for therange. Clinically, the purpose of the analyses reported here wasto address the question, Given the participant's highest subtestscaled score, what is the frequency of occurrence, or probability,of his or her lowest subtest scaled score relative to the normalsample?

    Method

    The participants were the 2,200 individuals of the WISC-ffl standard-ization sample described in detail in the WISC-III manual (Wechsler,1991). In brief, participants were children, ages 6 through 16 years,stratified on the basis of five demographic variables; age, gender, race-ethnicity, parent education, and geographic region of residence. Ouranalyses were derived from a data set that included subtest scale scores,IQ scores, and data for these five demographic variables.

    Ranges for subtest scaled scores were examined separately for theVerbal and Performance scales and for all WISC-III subtests. Highestand lowest subtest scaled scores were calculated for each participant,and frequencies for the entire sample were then calculated for eachlowest scaled score across the range of highest scores from 6 to 17+.Because there were so few highest scores of 18 and 19, scores of 17and above were combined for the frequency analyses.

    To expand further on Wechsler's (Wechsler, 1991) examination of theimportance of IQ level on subtest scatter, we examined the relativerelationships of highest subtest score and IQ to amount of subtest scatter.In addition, the amount of scatter was examined as a function of itsproportion of the potential range. If the amount of scatter is primarily

    a function of potential range, then the proportion should be relativelystable across highest subtest scaled scores.

    Results and Discussion

    Tables 1 through 6 present the frequencies of occurrence oflowest subtest scaled scores observed across the Rill, Verbal,and Performance scales classified by the highest subtest scaledscore for both the 10- and 12-subtest administrations. The tablesare organized so that they indicate the frequency of a particularvalue. Each entry shows the percentage of individuals whoselowest subtest scaled score is at or below that level. For example,the fourth column in Table 1 shows that for individuals with ahighest subtest scaled score of 14, only 1.7% had a lowestsubtest scaled score of 4 or less (i.e., a scatter range of 10 ormore) for the administration of five Verbal subtests.

    Examination of the mean scatter across highest scaled scoresindicates that scatter increases with larger values for the highestsubtest scale score. These results are consistent with those re-ported previously by Matarazzo et al. (1988) for the WMS-Rand by Kaufman (1976a, 1976b) and Reynolds and Gutkin(1981) for the WISC-R and Wechsler Preschool and PrimaryScale of IntelligenceRevised (WPPSI; Wechsler, 1989) stan-dardization samples, respectively. The correlation between FullScale scatter and highest subtest scaled score was .48 for the 10-subtest administration and .54 for the 12-subtest administration.Correlations between Full Scale scatter and Full Scale IQ were.06 and .07, respectively, for the 10- and 12-subtest administra-

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  • WISC-m SUBTEST SCATTER 87

    Table 6Full Scale (12 Subtexts, Digit Span and Mazes Included): Percentage of Cases by HighestSubtest Scaled Score at or Below the Value for the Lowest Subtest Scaled Score

    Lowestsubtestscaledscore

    16151413121110987654321

    n

    MSD%

    Highest subtest scaled score

    17+

    100.098.593.383.266.344.524.413.47.85.02.61.5

    4637.62.1

    59.9

    16

    100.099.699.697.592.877.662.040.922.410.13.83.01.3

    2376.92.0

    56.9

    15

    100.099.496.689.266.544.630.817.26.22.81.5

    3256.51.9

    57.0

    14

    100.099.798.693.280.158.139.223.616.29.13.7

    2965.82.1

    58.7

    13

    100.099.797.888.466.546.726.617.27.84.7

    3195.41.9

    58.1

    12

    100.095.987.364.540.824.111.45.3

    2454.71.7

    60.8

    11

    100.098.088.566.948.031.814.96.1

    1484.51.8

    59.5

    10

    100.097.792.078.451.128.418.2883.31.6

    66.6

    9

    100.084.863.043.530.4462.81.5

    68.9

    8 7 6

    100.096.076.060.0 100.052.0 83.325 6

    2.2 1.21.4 0.4

    72.5 82.9

    Note. M = mean lowest subtest score; SD = standard deviation of mean lowest subtest score; % =proportion of the possible scatter range accounted for by average scatter (mean scatter range/highest subtestscore). Standardization data of the WECHSLER INTELLIGENCE SCALE FOR CHILDRENTHIRDEDITION. Copyright 1990 by The Psychological Corporation. Used by permission. All rights reserved.

    tions. Thus, these results are consistent with those reported forthe WAIS-R by Schinka et al. (1994) and confirm the findingsof Wechsler (1991) concerning the relationship of IQ to scatterin the WISC-II1.

    Tables 1 through 6 also present the average amount of scatteras a percentage of potential scatter range (i.e., the average scatterdivided by the highest subtest scaled score). It is clear that theproportion of average scatter is relatively stable across highestsubtest scaled scores, at approximately 38% for the Verbal, 46%for the Performance, and 54% for the Full Scales for the 10-subtest administration. For the 12-subtest administration, thepercentages climb approximately 5 percentage points, as wouldbe expected because of the contribution of an additional subtestscore to the range of scatter.

    Tables 1 through 6 in this study provide the most precisetables available to help clinicians determine whether the amountof subtest scatter obtained in WISC-III clinical profiles is rareenough to be considered remarkable, and hence, of potentialclinical importance. In this regard, comments and caveats madeby other authors on the interpretation of scatter (e.g., Kaufman,1990) bear repeating. First, the base rate for any given level ofscatter is likely to be underestimated by most clinicians, espe-cially when considering scatter across both Verbal and Perfor-mance subtests. The use of tables, such as the ones providedherein, should be consulted whenever there is a question ofscatter of potential diagnostic significance. Second, even markedsubtest scatter is not necessarily indicative of pathology whenit constitutes the only evidence of neuropsychological deficit.Although it is possible that some participants in the WISC-III

    standardization sample with marked subtest scatter did in facthave undiagnosed pathology, it is very unlikely that all partici-pants with marked subtest scatter did. Even very marked subtestscatter is likely to reflect the state of normal individual differ-ences in many or most cases. Third, the meaning of markedscatter should only be addressed within the context of theWISC-III subtests under consideration, the assessment ques-tion, and all of the assessment (including remaining WISC-IIIsubtests), medical, neurological, psychological, and psychoso-cial information.

    An example may be useful. A scatter range of 9 within theVerbal subtests in the 10-subtest administration is in itself nota meaningful finding. In contrast, a highest scale score of 14on Vocabulary or Comprehension combined with a lowest scalescore of 5 on Arithmetic (base rate of occurrence of thesehighest-lowest score values = 3.3%; see Table I) would beconsistent with an arithmetic learning disability in the courseof a learning disability evaluation.

    References

    Black, F. W. (1974). Cognitive effects of unilateral brain lesions second-ary to penetrating missile wounds. Perceptual and Motor Skills, 38,387-391.

    Doehring, D. A., Reitan, R. R., & Klove, H. (1961). Changes in patternsof intelligence test performance associated with homonymaus visualfield defects. Journal of Nervous and Mental Disease, 132, 227-233.

    Kaufman, A. (1976a). A new approach to the interpretation of testscatter on the WISC-R. Journal of Learning Disabilities, 9, 160-168.

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    f the

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  • SCHINKA, VANDERPLOEG, AND CUKTISS

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    Kaufman, A. S. (1990). Assessing adolescent and adult intelligence.Boston: Allyn & Bacon.

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    McLean, J. E., Kaufman, A. S., & Reynolds, C. R. (1989). Base rates forWAIS -R subtest scatter as a guide for clinical and neuropsychologicalassessment. Journal of Clinical Psychology, 45, 919-926.

    Reynolds, C. R., & Gulkin, T. B. (1981). Test scatter on the WPPSI:Normative analyses of the WPPSI. Journal of Learning Disability,14, 460-464.

    Saltier, J. M. (1988). Assessment of children (3rd ed.). San Diego:Author.

    Schinka, J. A., Vanderploeg, R. D., & Curtiss, G. (1994). WAIS-Rsubtest scatter as a function of maximum subtest scaled score. Psycho-logical Assessment, 6, 364-367.

    Silverstein, A. B. (1987). Two indices of subtest scatter on Wechsler'sintelligence scales: Estimated vs. empirical values. Journal of ClinicalPsychology. 43, 409-414.

    Silverstein, A. B. (1989). Reliability and abnormality of scaled-scoreranges. Journal of Clinical Psychology, 45, 926-929.

    Simpson, C. D., & Vega, A. (1971). Unilateral brain damage and pat-terns of age-corrected WAIS subtest scores. Journal of Clinical Psy-chology, 27, 204-208.

    Wechsler, D. (1981). Manual for the Wechsler Adult IntelligenceScaleRevised. New "York: Psychological Corp.

    Wechsler, D. (1989). Wechsler Preschool and Primary Scale of Intelli-genceRevised. San Antonio, TX: The Psychological Corporation.

    Wechsler, D. (1991). Manual for the Wechsler Intelligence Scale forChildrenThird Edition. New York: Psychological Corp.

    Received June 10, 1996Revision received September 30, 1996

    Accepted October 12, 1996

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