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Allyson G. Harrison, Ph.D, C.Psych

A Validation Of The Dyslexia Adult Screening Test (DAST) in A Post Secondary Population. Allyson G. Harrison, Ph.D, C.Psych. Dyslexia Adult Screening Test DAST. Developed by Fawcett & Nicholson in UK Published by Psych corp 1998

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Allyson G. Harrison, Ph.D, C.Psych

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  1. A Validation Of The Dyslexia Adult Screening Test (DAST) in A Post Secondary Population Allyson G. Harrison, Ph.D, C.Psych

  2. Dyslexia Adult Screening Test DAST • Developed by Fawcett & Nicholson in UK • Published by Psych corp 1998 • Normative data collected on 550 “normal” students & 618 adults (age 17-65). • ? # Dyslexic subjects-No reference at all. • At Risk Quotient (ARQ) calculated based on performance on 11 subtests

  3. The Dyslexia Adult Screening Test (17+ yrs)

  4. DAST cut-offs • ARQ of .7 or more = slightly at risk • ARQ of 1 or more = highly at risk Fawcett & Nicholson used the cut off of 1.0 in their normative study!

  5. Problems with initial norms • “Dyslexic Student” data consists of only 15 people • Dyslexia validated by ADI: ACID pattern on WAIS; spelling, nonsense passage reading & previous hx dyslexia. • ARQ calculated dividing by 9 instead of 11 • How well can DAST accurately identify Dyslexic students based on this limited sample?

  6. Current study • LOTF project in Ontario, Canada • Improve services & supports for “Dyslexic” students in post-secondary. • Pilot students had to meet rigorous diagnostic criteria for inclusion: • 2 std dev difference between measure of intellectual potential & achievement &/or specific information processing skill, + consistent history

  7. Subjects • 117 “well validated” Pilot students • 122 volunteer controls • Sex ratio equal in Pilot students, but 75% of controls were female. • Mean age of two groups equal

  8. Results Using .7 as cut off (mild risk): • 85% of Dyslexics correctly identified • 15% missed. 3 subjects had ARQ < 0.01 • 25% “controls” identified as mild risk Using 1.0 (high risk) as cut off: • 74% Dyslexics correctly identified • 15% controls identified as high risk

  9. Hit rate by subtest( ARQ>.99)

  10. Information about control subjects • Recruited from first-year courses, posters, and work-study student population • Completed self-rating scales & DAST • Correlation between self-rated reading pleasure and ARQ=.40 • Correlation between self-rated reading skills and ARQ=.52

  11. Relationship Between Pleasure from Reading and ARQ (Control gp only) 3.00 2.50 2.00 2 R = 0.1585 1.50 At Risk Quotient (ARQ) Highly at risk cut off 1.00 0.50 0.00 1 2 3 4 5 Self-rated reading enjoyment (1=very pleasurable; 5=no pleasure)

  12. Relationship Between Self-rated Reading Skills and ARQ (control gp only) 3.00 2.50 2.00 2 R = 0.2722 1.50 At Risk Quotient (ARQ) Highly at risk cut off 1.00 0.50 0.00 1 2 3 4 5 Self-rated Reading skill (1=strongest; 5=poorest)

  13. Self-reported Academic Weaknesses (Control group)

  14. ARQ scores for control subjects who reported reading problems ARQ 0.20 0.36 0.63 0.27 0.36 0.18 0.82 0.82 0.90 1.45 1.09

  15. Recalculation of DAST • Remove postural stability (least consistent & lowest inter-rater agreement) • Remove subtests with largest group overlap • Remove subjects with NVLD • Recalculate ARQ based on 7 subtests

  16. Recalculated DAST (Excluding subtests 3, 8 & 11 + NVLD) Using .7 as cut off (mild risk): • 88 % of Dyslexics correctly identified • 12 % missed. • 27 % “controls” identified as mild risk Using 1.0 (high risk) as cut off: • 77 % Dyslexics correctly identified • 17 % controls identified as high risk

  17. Conclusions • DAST in present form is not acceptable as screening for LD • Good screening test should identify almost ALL of true Dyslexic subjects. This does not. • Removal of subtests with questionable discriminate validity improves hit rate slightly, but still misses 12% of Dyslexic students • Relationship between ARQ & criterion variables (such as self-rated reading skill) an issue

  18. Suggestions • Investigation of IQ-ARQ correlation • Establish criterion validity of ARQ & subtests in non-disabled control group • Recalculation of normative scores and cut offs using larger Dyslexic sample. • Don’t throw the baby out with the….

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