Use of the Wechsler scales in specialized assessments: news from the trenches

1. Use of the Wechsler scales in specialized assessments: news from the trenches Dr. Allyson G. Harrison Regional Assessment & Resource Centre

2. WAIS as Dx instrument • Wechsler IQ test never designed to diagnose a neuro disorder. Many people searched for patterns, but no one pattern to date is diagnostic. • Matarrazo (1984,1988,1989,1990,1992), Gnys & Faust (1995) • Best for generating or testing hypotheses

3. Problems with certain populations • Overall IQ from Wechsler scales may not be accurate in certain groups, especially where processing speed or wm problems • Eg. LD, brain injury/disorder,motor • “mark penalty” (Dumont & Willis) • Need way to reduce influence on FSIQ in these populations

4. PS & WM • Many people with LD have problems not with thinking but with PS or WM • proc spd like modem spd on computer. Compare two computers of equal ability in time-limited environment, requiring them to link to internet. • WM & PS are not “intelligence”, but can limit what people can demonstrate

5. Minimize influence of WM & PS • Want way to partial out or factor out the effect of slow proc spd or poor working memory from obtained scores. • Current FSIQ doesn’t do this • Current factor score approach doesn’t do this.

6. GAI • Suggested as better indicator of general ability or “g” than FSIQ • Highly correlated with crystallized & fluid factors of WAIS. • More resilient to brain insults or neurological disorders • Based on normative data from WAIS-III • Has better incremental validity (vs. full WAIS) if you just want estimate of “g” • Easy to calculate

7. Present study • 262 students aged 17-57 (median 20yrs) • Data collected between 2002-2004 • Referred for psycho educational or neuropsychological assessment due to academic difficulties • Enrolled at (or accepted into) college or university • 134 females, 128 males

8. Diagnoses • All referred b/c of suspected LD, ADHD or HI • 80/262 LD (31%) • 79/262 ADHD (30 %) • 12 HI (5 %) • 14 Depressed (5 %) • 18 Anxiety (7 %) • 13 Chronic PTSD (5 %) • 45 Other/No DX (17%) • 15% received dual diagnoses

9. Dx Criteria • LD=LDAO definition criteria • No use of GAI • Other historical data congruent • Other causes ruled out • ADHD=DSM IV criteria (past & present) • Including exclusion criteria met • May or may not have been on meds at time

10. FSIQ-GAI

11. FSIQ-GAI for LD group

12. GAI-DWI2 (proc & WM index)

13. Criteria for use of GAI

14. Support for use of GAI • Appears useful in assessments where PS or WM interfere with scores • Good if want overall measure of intellectual potential with minimal influence of these factors • Use more lenient decision rules for determining when to use GAI (statistical significance of either VIQ-PIQ, oreither of VC-WM or PO-PSI)

15. What about factor scores? • Current FS system: one test = one skill • Formula. Says VOC, SIM, INFO measure VC and nothing else. • BD, PC, MR measure only PO and nothing else • PS=Symbol search or Digit symbol • WM=Arith, Dspan, LNS

16. Subtests not “pure” measures • Score on BD = not just PO, but also WM, Proc spd and some VC • Sim score not just VC, but also PO (and to some extent PS & WM) • MR is not just PO. Also contains WM and VC • Four current index scores, as normally calculated, are interdependent

17. Equal or differential weights Parker and Atkinson (1995), and Caruso and Cliff (1999) • Factor analysis of WAIS data. Evaluated the extent to which each subtest is saturated with components of each skill, and partial these out. Obtain purer measure of each skill.

18. Sample component loadings .87 vc Voc .84 .74 .19 PO .16 Info .30 .20 .23 WM Sim .17

19. Restructured Factor scores • Derived from rotated 4 solution factor analysis of WAIS-III normative data • calculated by differential weighting (rather than equal weighting as in the WAIS factor scores). • Each factor minimally influenced by “g” or by other factors • High correlation with existing “corresponding” factors, but not with other factors (eg. PSI & PS (RCA) correlate .87).

20. Interrelations between factors

21. Difference between weighted and unweighted factors

22. Difference between weighted and unweighted factors

23. Conclusions • WAIS-III GAI almost always better estimate of intellectual potential in neurologically compromised groups. • Give all subtests of WAIS if want more than estimate of “g” • Present equal weighted factors provide little incremental information over “g” due to high intercorrelations with “g” • Weighted factor scores provide greater incremental information, due to lack of overlap between factor scores

24. Conclusions • RCA factor scores better at demonstrating real differences between processing skills in neurologically compromised groups • Differences between RCA factor scores more reliable than those between equal wt factor scores • Only problem: more complicated to calculate.