A Validation Of The Dyslexia Adult Screening Test (DAST) in A Post Secondary Population

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

The Dyslexia Adult Screening Test (17+ yrs)

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!

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?

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

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

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

Hit rate by subtest( ARQ>.99) DAST subtestDyslexic students (N=117) Incidence (%) Control Students (N=122) Incidence (%) Rapid Naming One Minute reading Postural stability Phonemic Segmentation minute spelling Backward Digit span Nonsense passage Non-verbal reasoning minute writing Verbal fluency Semantic fluency

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

Relationship Between Pleasure from Reading and ARQ (Control gp only) R 2 = Self-rated reading enjoyment (1=very pleasurable; 5=no pleasure) At Risk Quotient (ARQ) Highly at risk cut off

Relationship Between Self-rated Reading Skills and ARQ (control gp only) R 2 = Self-rated Reading skill (1=strongest; 5=poorest) At Risk Quotient (ARQ) Highly at risk cut off

Self-reported Academic Weaknesses (Control group) Area of academic difficulty Percentage who endorsed Math43.4% Study skills26.2% Memory21.3% Spelling18% No area of difficulty16.4% Organizational skills11.5% Reading9%

ARQ scores for control subjects who reported reading problems ARQ

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

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

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

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….