Stewart questioned Beglar's use of Rasch analysis of the Vocabulary Size Test (VST) and advocated the use of 3-parameter logistic item response theory (3PLIRT) on the basis that it models a non-zero lower asymptote for items, often called a "guessing" parameter. In support of this theory, Stewart presented fit statistics derived from…

Diagnostic hit rates for the Diagnostic Inventory of Personality and Symptoms were compared to diagnosis by psychiatrists of the same patients. The Probability Scale employing Bayesian concepts and base rates correctly classified 70% of the patients and was more accurate by far than the other two methods used. (Author/ABB)

The author argues against the accepted symptom of learning disabilities--a discrepancy between measured intelligence and measured educational achievement scores; and demonstrates that it is feasible to produce a quantitative definition of educational underachievement, and therefore to identify learning disabled students. (SBH)