Intra Ability Discrepancy Model

Unique to the WJ III are three types of norm-based within-person discrepancy score procedures that have the potential to better identify the unique patterns of cognitive abilities and achievements in individuals with LD. Collectively the intra-cognitive, intra-achievement, and intra-individual (cognitive and achievement combined) discrepancies are called the intra-ability discrepan

6The term aptitude has come to be misunderstood in much of psychological practice. Snow (1991) provides an excellent summary of the history of how the original connotation has changed (for the worse) over time. The term aptitude is used here in the classic sense as described by Snow.

cies. The intra-ability discrepancies allow examiners to analyze an individual's cognitive and academic strengths and weaknesses across the cluster scores of the WJ III COG and WJ III ACH. These discrepancies, and the combined COG and ACH procedure in particular (intra-individual), can assist in the identification of a learning disability by providing information that complements (but does not supplant) the information provided by the GIA and PA ability— achievement discrepancies.

The logic of intra-ability discrepancies is simple. Using the intra-cognitive discrepancies as an example, the standard score for each of the seven CHC cognitive clusters is first isolated (the target cluster) from the six remaining clusters, which are then averaged. The average of the "other" cognitive clusters then functions similarly to the ability cluster in the GIA Ability-Achievement Model previously described and presented in Figure 14.3. The average of the "others" generates a predicted score for the isolated target cluster. A discrepancy between the target cluster standard score and the predicted standard score is calculated and the result compared against the distribution of discrepancy norms for the target cluster. The same discrepancy evaluation scores (percentile rank and standard deviation units) provided for the GIA and PA Models are used to interpret the importance of the intra-cognitive discrepancy. The intra-achievement and intra-individual (achievement and cognitive clusters combined) discrepancy norms are derived from similar procedures.

Schrank and Mather (2001) believe that the intra-individual discrepancy procedure may be particularly useful in the identification of a specific learning disability when the examiner needs to determine what is "specific" about the problem. The intra-individual procedure is conceptually similar to recent recommendations to identify an individual with a learning disability via the evaluation of domain-specific achievement skills conjointly with their related cognitive abilities (Brackett & McPherson 1996; Fletcher et al., 1998). For example, an adolescent referred for long-standing problems with math who demonstrates relative intra-individual weaknesses (less than -1 SD) on the WJ III ACH Math Calculation and Math Reasoning clusters with concurrent deficits on the WJ III COG Working Memory (Gsm), Long-term Retrieval (Glr), Processing Speed (Gs), and Fluid Reasoning (Gf) clusters would be exhibiting a constellation of deficits consistent with a domain-specific disability in mathematics (Carroll, 1996; Geary, 1993; Geary, Hamson, & Hoard, 2000; Geary, Hoard, & Hamson, 1999). The intra-individual discrepancy procedure can be used with several combinations of clusters depending on which sets of WJ III COG and ACH tests are administered.

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