The development of the WISC-Ill (Wechsler, 1991), a revision of the Wechsler Intelligence Scale for Children-Revised (WISC-R; Wechsler, 1974), was prompted by the need for current normative information, updated stimulus materials, improvement in the fairness of the test, and an enhanced factor structure (Prifitera, Weiss, & Saklofske, 1998).
The WISC-Ill contained several changes to the WISC-R, including the ad- dition of several new subtests. The addition of these subtests enhanced the interpretive structure of the test to include not only Full Scale, Verbal, and Performance IQ scores but also four factor-based Index scores: Verbal Com- prehension, Perceptual Organization, Freedom from Distractibility, and Pro- cessing Speed (Wechsler, 1991).
Currently, the WISC-III is composed of 13 subtests, 3 of which are supple- mental or optional. Following the WISC-R model, the WISC-III is organized into two primary scales: Verbal and Performance. The Verbal Scale contains subtests that provide a measure of verbal reasoning skills that are primarily reflective of acquired knowledge: Information, Similarities, Arithmetic, Vo- cabulary, Comprehension, and Digit Span (optional). The Performance Scale, on the other hand, provides a measure of nonverbal reasoning and percep- tual-motor skills: Picture Completion, Coding, Picture Arrangement, Block Design, Object Assembly, Symbol Search (optional), and Mazes (optional).
(See Table 1.1.)
The four factor-based indexes contain different compositions of the Verbal and Performance scales. The Verbal Comprehension Index is composed of subtests that provide a purer measure of verbal reasoning skills: Informa- tion, Similarities, Vocabulary, and Comprehension. Those subtests that are also part of the Verbal Scale but load on another factor, Freedom from Distractibility, are Arithmetic and Digit Span. The Perceptual Organization Index contains several Performance Scale subtests that are purer measures
TABLE 1.1
WISC~IIi Subtests and Description
Verbal scale Construct Performance scale Construct
Subtest Subtest
Information Factual knowledge Picture Completion
Similarities Verbal concept Coding formation
Arithmetic Auditory memory Picture Arrangement and attention
Mental computation
Vocabulary Fund of information Block Design
Comprehension Use of practical Object Assembly judgment in social
situations
Digit Span Short-term auditory Symbol Search memory
Mazes
Ability to differentiate salient from nonsalient visual information Psychomotor speed Planning ability and attention to detail Spatial visualization and visual-motor coordination Ability to synthesize
concrete parts into meaningful wholes Attention and processing
speed
Planning ability and visual-motor coordination Source: From Assessment of Children: Revised and Updated Third Edition, by J. M. Sattler, 1992, San Diego, CA: Author.
of nonverbal reasoning skills: Picture Completion, Picture Arrangement, Block Design, and Object Assembly. The subtests Coding and Symbol Search, which constitute the Processing Speed Index, are also part of the Perfor- mance Scale.
WISC~lll Scores and Interpretive Paradigms WISC~lll Hierarchical Analysis
The WISCrlII Full Scale, Verbal Scale, and Performance Scale IQ (FSIQ, VIQ, and PIQ, respectively) scores as well as the four index scores have a mean of 100 and a standard deviation of 15. Each of the 13 subtests has a mean of 10 and a standard deviation of 3.
The derivations of the IQ and Index scores lend themselves to a hierarchi- cal interpretive sequence: FSIQ, VIQ-PIQ, index scores, and individual subr tests (Kaufman, 1994). According to Kaufman (1994), the recommended pro- cedure for analyzing a child's performance can be summarized in seven steps.
Step One involves the interpretation of the FSIQ. The FSIQ provides a mea- sure of overall functioning; however, large discrepancies between a child's performance on the Verbal and Performance scales, or large fluctuations on subtest performance within each of these scales, may lessen the weight that is given to the FSIQ as an indication of global performance. To illustrate, if a child obtains a Verbal IQ score of 85 and a Performance IQ score of 115, the FSIQ score of 99 would not adequately represent the functioning of the child given the 30rpoint disparity between the child's verbal and nonverbal rear soning skills.
Step Two involves the analysis of statistically significant discrepancies bet tween Verbal and Performance IQ scores (i.e., VIQ~PIQ). The base rate (cur mulative percentage of students in the standardization sample obtaining that VIQ~PIQ difference or lower) should also be examined in order to deter- mine whether the statistical difference is clinically significant. For example, if 32% of the standardization sample obtained a 13-point or lower difference between the VIQ and PIQ scores, a statistically significant difference would be less meaningful in its clinical interpretation because this difference was ob- tained by a large percentage of the standardization sample. In fact, the clini~
cian may wish to deemphasize the difference because this discrepancy is fairly common within the normal population.
Step Three involves the determination of whether the VIQrPIQ discrepancy should be forfeited in favor of the more factorial pure verbal and performance factors, Verbal Comprehension (VC) and Perceptual Organization (PO). In or- der to assess whether this kind of interpretation is warranted, the four factors should be analyzed within their respective scales. For instance, as described earlier in the chapter, VC and Freedom from Distractibility (FD) constitute the Verbal Scale. If these two factor scores are markedly discrepant from each
other, the VIQ does not provide a representative picture of the child's perfor- mance in this domain; VC may be a better indicator of verbal reasoning in this regard. On the other hand, if a child's performance is variable across the two factor scores that constitute the PIQ, PO and Processing Speed (PS), PO should be reported in lieu of the PIQ. In fact, both the VC and PO factors are purer measures of each of the verbal and performance domains than the VIQ and PIQ, respectively. As a result, the clinician may wish to describe student performance within the context of these larger factors only.
Step Four involves the additional analysis of VC and PO discrepancies; this analysis is similar to the VIQ-PIQ discrepancy analysis in the determination of statistically and clinically significant differences.
Step Five includes the interpretation of the global verbal and performance domains in light of the two smaller factors: PS and FD. In instances in which the VIQ and PIQ are forfeited in favor of the two larger and two smaller fac- tors, the factor scores should be used for interpretive purposes in lieu of reporting the VIQ, PIQ, or FSIQ. Practically, this situation may present a dilemma for the clinician because most diagnostic and placement decisions (e.g., diagnosis of mental retardation) are made on the basis of an overall IQ score. However, from the standpoint of meaningful interpretation regarding the cognitive processing strengths and weaknesses of the child, the descrip- tion of performance within factor domains is the most defensible.
Steps Six and Seven address the interpretation of individual subtests and any fluctuations in subtest performance within each of the factor indexes as well as within the more global Verbal and Performance scales. As a general interpretive rule, individual subtest scores can be compared to the mean scaled score within their respective Verbal and Performance scales. Again, both statistical and clinical considerations must be taken into account in the interpretation of significantly discrepant scores. In cases in which the perfor- mance of the child varies greatly across the Verbal and Performance scales as well as factor domains, the most appropriate interpretation of the child's strengths and weaknesses lies in a subtest by subtest analysis. For example, if the child has subtest scores that are statistically significantly different from each other within a factor (e.g., Comprehension, Similarities, and Informa- tion in the Verbal Comprehension factor), the child's performance would sug- gest that there is significant variability within this domain. If a child obtains an above average score on Information, an average score on Comprehension, and a below average score on Similarities, the clinician may conclude that the child has a good fund of factual knowledge and can make reasonable judgments within a social context, but is experiencing difficulty with more abstract verbal reasoning tasks. This level of interpretation (at the subtest level) would be more appropriate than describing the child's performance at the factor level (e.g., the child demonstrates verbal reasoning skills within the average range).
In an analysis of the correlations of the individual subtests with overall IQ,
Kaufman (1994) further recommends that the optional subtest, Symbol Search, be substituted for Coding because Symbol Search correlates more highly with Performance IQ (Symbol Search, .58; Coding, .32) and has higher loadings on the Perceptual Organization factor than Coding (.54 vs..39). Sub~
sequent research studies (Reynolds, Sanchez, & Willson, 1996; Saklofske, Hildebrand, Reynolds, & Willson, 1998) have substituted Symbol Search for Coding in the calculation of norms and have provided normative tables for the calculation of Performance and Full Scale IQ scores for both the Ameri- can and Canadian standardization data.
The hierarchical analysis (as recommended by Kaufman, 1994) is readily expedited through the use of computer scoring assistants and interpretive software (e.g., WISC-III Writer, 1994, and Scoring Assistant for the Wechsler Scales [SAWS], 1992). These computer programs include both statistical and base rate analyses. The WISC-III Writer also provides interpretive clinical and parent reports that can serve as a basis for the clinician's assessment reports.
General Ability Index
Overall, the addition of the third and fourth factor indexes on the WISC-III has facilitated the shift from an overreliance on the three IQ scores (FSIQ, VIQ, and PIQ) to more of a factor-based interpretation of performance. In fact, Pri- fitera, Weiss, and Saklofske (1998; see also Weiss, Saklofske, Prifitera, Chen,
& Hildebrand, 1999) have proposed an alternative way of summarizing over~
all performance using a composite score, the General Ability Index (GAI), based upon the Verbal Comprehension Index and the Perceptual Organiza- tion Index. The GAI is recommended for use rather than the FSIQ under any one of the following conditions: (a) when the VC is reported in favor of the VIQ (e.g., when Arithmetic is significantly different from the average of the other Verbal scaled scores), (b) when the PO is interpreted in favor of the PIQ (e.g., when Coding is significantly discrepant from the mean of the other Per- formance scaled scores), and (c) when the VC and PO factor indexes are re- ported in lieu of the VIQ and PIQ. The utility of the GAI is comparable to that of the FSIQ in determining eligibility for services and placement decisions;
however, the GAI may result in a higher estimate of overall functioning if the child has obtained Arithmetic and/or Coding scores that are significantly lower than the other subtest scores--these scores would contribute to a lower FSIQ score (Prifitera, Weiss, and Saklofske).
A Priori and A Posteriori Hypothesis Testing
According to Kamphaus (1993, 1998), test interpretation based upon the four factors of the WISC-III has greater scientific support than interpretation based upon individual subtests. Empirical evidence and theoretical consid- erations can drive both a priori and a posteriori hypothesis generation and
testing. Test interpretation can begin at the early stages of the assessment process and involves the generation of theoretically and research~driven hypotheses prior to the calculation of test scores. The hypotheses can then be tested against the data that are derived. Alternatively, a posteriori hy- potheses allow the review of obtained scores within the context of support~
ing evidence based upon both research and theoretical information. Both nor methetic and idiographic approaches may be taken in the generation of a posteriori hypotheses. For example, the child's pattern of performance may be compared to his or her peers' within the standardization sample, or alter- natively may be assessed within the context of his or her individual strengths and weaknesses. Testing of limits (e.g., administering items in a nonstanr dardized fashion after the completion of the initial test administration) al- lows generation of hypotheses based upon an idiographic approach.
A caveat should be noted, however, in the interpretation of the four factors on the WISC~III. The third and fourth factors, Freedom from Distractibility and Processing Speed, each consist of only two subtests. As a result, these factor scores break down more readily than the larger factors due to the small num- ber of subtests that contribute to each. Also, the third factor's descriptor, Freedom from Distractibility, is a misnomer, because scores on the third fac- tor do not necessarily correlate with other measures of attention (Lowman, Schwanz, & Kamphaus, 1996; Riccio, Cohen, Hall, & Ross, 1997).
THE WISC-II! PI
The WISCrlII PI was developed to supplement the standard test administrar tion of the WISC-III (Kaplan et al., 1999). As stated in the introduction to this chapter, the WISC-III PI takes a process approach to the interpretation of a child's performance on the WISC-III tasks. Its purpose is to serve as "a means of identifying the strategies that are employed to solve a task as well as a means of examining the nature of the errors made, the particular context in which they occurred, and the nature of the stimulus parameters" (Kaplan et al., p. 4).
The WISC~III PI incorporates several approaches to obtaining informar tion on a child's strategies: Current WISC-III subtests are given with alterna- tive or supplemental procedures for scoring, current WISC-III subtests are given with add-on procedures, subtests equivalent to the WISC-III are adz ministered with alternative formats, and new subtests are administered with administration formats similar to those of the WISC-III but with different con~
tent (Kaplan et al., 1999). Current WISC-III subtests that have additional scor- ing procedures include Picture Completion, Information, Coding, Arithme- tic, Block Design, Vocabulary, Digit Span, and Picture Arrangement. Subtests with addron administration procedures are Coding and Arithmetic. Supple r mental components of current WISC-III subtests include Information Mul- tiple Choice, Coding-Symbol Copy, Written Arithmetic, Block Design Mulr
tiple Choice, Vocabulary Multiple Choice, and Picture Vocabulary. New sub- tests on the WISC-III PI are Letter Span, Spatial Span, Elithorn Mazes, and Sentence Arrangement.
Alternative administration and scoring formats and parallel subtests al- low additional analyses of a child's cognitive processing strengths and weak- nesses. For example, the Block Design subtest on the WISC-III PI is a multiple choice task (rather than a block manipulation task); the motor component is removed to allow assessment of visual-perceptual skills without the con- found of visual-motor coordination difficulties.
The newness of the WISC-III PI has precluded a review of the test's prop- erties and applications in independent research studies; however, the test authors have identified several applications of the WISC-III PI in the test manual:
1. Investigation of reasons for low WISC-III subtest scores.
2. Systematized observation of a child's problem-solving approaches.
3. Derivation of a detailed profile of a child's strengths and weaknesses.
4. Analysis of a child's performance for the purposes of diagnostic deci- sion making (e.g., determination of neurodevelopmental disorders).
5. Establishment of a baseline for evaluating improvement or decline in functioning over time.
6. Implementation of the test as a research tool in the areas of neuro- logical and developmental disorders.
THE CMS
The Relationship between Intellectual Functioning and Memory
While the WISC-III is primarily a measure of prior or past learning and infor- mation processing, the CMS is a novel measure of new learning and memory.
The concept of memory is closely associated with learning because memory is the natural outcome of learning. Squire (1987) provides an excellent defini- tion of learning and memory: "Learning is the process of acquiring new in- formation, while memory refers to the persistence of learning in a state that can be revealed at a later time" (p. 3). The traditional or most common mem- ory distinction is short- versus long-term memory. Short-term memory refers to a temporary storage (usually from only seconds to 1-2 minutes), whereas long~term memory refers to the permanent or more stable storage of memo- ries. The process by which information is transformed into mental represen- tations is referred to as encoding. The process of bringing stored information into conscious awareness, or remembering, is referred to as retrieval.
A further categorization of delayed or long-term learning and memory is into either procedural or declarative memory. Procedural memory effects a change in a person's behavior on the basis of experiences without the person
necessarily having conscious access to the events that produced the change in behavior. These behaviors, such as riding a bicycle, are performed auto~
matically. In contrast, declarative memory is the ability to store and retrieve specific elements of information or knowledge. Declarative memory can be further divided into semantic and episodic memory. Semantic memory in- volves memories for general facts and concepts. Episodic memory involves information that is situation- and context~specific. Within this conceptual framework, the CMS is primarily a measure of declarative episodic memory.
In other words, the information that is presented in the CMS is novel and con- textually bound by the testing situation (i.e., situation/context specific) and requires the examinee to retrieve newly learned information.
Discrepancies between general intellectual ability and memory can be used to evaluate an individual's current memory functioning. Because of the relatively high correlation between IQ and memory (e.g., FSIQ-General Memory Index r - .58) (Cohen, 1997), the individual's IQ scores become an index or estimate of his or her probable level of memory ability. Discrepan- cies between the estimated memory performance based on IQ scores and the individual's actual memory performance form the foundation for the discrep- ancy analysis. The discrepancy score then provides a global indication of whether the examinee's ability to learn and remember new material is com- mensurate with what would be expected on the basis of his of her intellectual functioning. The interpretation of differences between intellectual and mem- ory functioning follows the same logic and methodology used in the inter- pretation of ability-achievement discrepancies. An essential criterion for the appropriateness of score comparisons is the comparability of the normative data for the two test measures. That is, they should be highly comparable or identical. Because the CMS was directly linked to the WISC-III, direct com~
parisons based on the same normative data can be made.
Historical Development of the CMS
The CMS was developed to fill the previous void of comprehensive and well- normed instruments in the area of learning and memory in children (Cohen, 1997). According to Cohen, traditional psychoeducational assessment proto- cols included tests for intellectual functioning, achievement, and behavior, but did not assess the area of new learning and memory despite the fact that most referrals were related to the inability of the child to learn and remem- ber school~related content. As a result, most of the diagnostic information gleaned from the test data was limited in scope (e.g., Digit Span on the WISC- III) or inferential in nature (e.g., clinical observations).
The CMS was designed to address five issues:
1. The development of an instrument that was predicated on current theoretical models of learning and memory.