Introduction to the WAIS-III / WMS-III Demographically Adjusted Norms 6-Factor Model Analysis Tool
The 6-Factor Model (Tulsky, Ivnik, Price, & Williams, 2003) is an alternate model for creating composites from WAIS–III / WMS–III subtests. The model is based on the WAIS–III / WMS–III joint factor structure. The subtests used in the 6-Factor configuration of indexes differ from those used in the WAIS–III/WMS–III Scoring Assistant. Researchers must decide which memory index scores are most applicable in their research. See Tulsky et al. (2003) for the rationale and normative tables for these composites.
The six factors and contributing subtests used in this model include:
- Verbal Comprehension
- Block Design
- Matrix Reasoning
- Picture Completion
- Letter-Number Sequencing
- Spatial Span
- Digit Symbol-Coding
- Symbol Search
- Logical Memory I
- Logical Memory II
- Paired Associates I
- Paired Associates II
- Family Pictures I
- Family Pictures II
- Visual Reproduction I
- Visual Reproduction II
The 6-Factor Model substitutes Visual Reproduction for Faces and organizes the memory subtests by sensory domain (auditory and visual), rather than by immediate and delayed conditions. It is not fully clear if this model better reflects the neurological structure of memory or an artifact related to the statistical interdependence of the immediate and delayed memory tasks within each sensory modality. More research of the underlying structure of memory and brain-imaging studies are needed before firm conclusions can be made about the composition of the memory composites.
The demographically adjusted norms are derived from the application of fractional polynomial regression procedures (Royston & Altman, 1994), to the standardization and education/ethnicity over-sample cases from the WAIS–III/WMS–III. The adjusted norms adjust the six WAIS–III/WMS–III Composite Scores for Age (20–89 years), Education Level (7–17 years), Ethnicity (African-American, Hispanic, and Caucasian only) and Sex, for individuals educated primarily in the U.S.
The demographically adjusted scores are most appropriately applied in the context of a neurodiagnostic assessment to minimize the impact of psychosocial variables on the diagnosis of cognitive impairment, such as estimating the degree of cognitive impairment after a brain injury or insult. The demographically adjusted scores are not intended for use in psychoeducational evaluations, determination of intellectual deficiency, vocational assessment, or in any context in which the purpose of the evaluation is to determine the absolute functional level (IQ or Memory) of the examinee relative to a representative sample of the U.S. population. To avoid confusion with traditional IQ and memory scores, the demographically adjusted scores are reported on a T-score metric with a mean of 50 and standard deviation of 10 scaled-score points.
The full demographically adjusted norms are interpreted as:
> 55 = Above Average
45–54 = Average
40–44 = Low Average
35–39 = Mild Impairment
30–34 = Mild to Moderate Impairment
25–29 = Moderate Impairment
20–24 = Moderate to Severe Impairment
< 20 = Severe Impairment
As a clinician, you should be familiar with the research studies and rationale for using demographically adjusted norms. You are responsible for the appropriate use of demographically adjusted norms and should exercise caution when interpreting the adjusted WAIS–III / WMS–III scores.
Royston, P. & Altman, D. G. (1994). Regression using fractional polynomials of continuous covariates: Parsimonious parametric modeling. Applied Statistics, 43, 429–467.
Taylor, M. J. & Heaton, R. K. (2001). Sensitivity and specificity of WAIS–III / WMS–III demographically corrected factor scores in neuropsychological assessment. Journal of the International Neuropsychological Society, 7, 867–874.
Tulsky, D. S., Ivnik, R. J., Price, L. R. & Wilkens, C. (2003). Assessment of Cognitive Functioning with the WAIS–III and WMS–III: Development of a Six-Factor Model. In D. S. Tulsky et al., (Eds.) Clinical Interpretation of the WAIS–III and WMS–III. San Diego: Academic Press.