Psychometric approaches to the identification of LD: IQ and achievement scores are not sufficient

Simulated data were used to demonstrate that groups formed by imposing cut-points based on either discrepancy or low-achievement definitions of learning disabilities (LD) are unstable over time. Similar problems were demonstrated in longitudinal data from the Connecticut Longitudinal Study, where 39% of the children designated as having LD in Grade 3 changed group placement with repeated testing in Grade 5. These results show that the practice of subdividing a normal distribution with arbitrary cut-points leads to instability in group membership. Approaches to the identification of children as having LD based solely on individual test scores not linked to specific behavioral criteria lead to invalid decisions about individual children. Low-achievement definitions are not a viable alternative to IQ-discrepancy definitions in the absence of other criteria, such as the traditional exclusions and response to quality intervention. If we accept the premise of multiple classes of low achievers, then we must develop identification systems that are valid and abandon systems whose only merits are their historical precedence and convenience.     

Cerebellar tests differentiate between groups of poor readers with and without IQ discrepancy

A comprehensive test battery, including phonological, speed, motor and cerebellar tasks, was administered to the entire cohort of two schools for children with learning disabilities. Testing was undertaken blind without accessing the psychometric data on the children. Children were then allocated to a discrepancy group on the basis of their IQ, with the majority (n = 29) classified as nondiscrepant (IQ < 90) and a smaller set (n = 7), with IQ of at least 90, classified as discrepant (with dyslexia). Both groups showed significant deficits relative to age-matched controls on almost all the tests. On phonological, speed, and motor tasks, the nondiscrepant group were at least as severely impaired as the discrepant group. By contrast, on the cerebellar tests of postural stability and muscle tone, the nondiscrepant group performed significantly better than the children with dyslexia and close to the level of the controls. The findings indicate that cerebellar tests may prove a valuable method of differentiating between poor readers with and without IQ discrepancy. The findings are interpreted in terms of the cerebellar deficit hypothesis for dyslexia.     

The relationship between achievement and IQ in students with learning disabilities

To investigate the relationship between achievement and IQ in the learning-disabled (LD) population, changes in the IQ scores of LD students from the early elementary grades to the high school grades were studied. The intercorrelations among those IQ scores and a variety of achievement scores were then explored for the purpose of ascertaining causal relationships. The results were interpreted as support for the contention that the underachievement of LD students (in particular, reading underachievement) plays a predominant causal role in the achievement-IQ relationship in this population.     

IQ and neuropsychological predictors of academic achievement

Word reading and math computation scores were predicted from Wechsler Abbreviated Scale of Intelligence Full Scale IQ, 10 neuropsychological tests, and parent attention deficit hyperactivity disorder (ADHD) ratings in 214 general population elementary school children. IQ was the best single predictor of achievement. In addition, Digit Span contributed significantly to reading prediction, and the Developmental Test of Visual-Motor Integration (VMI) and Coding contributed to math prediction. The remaining neuropsychological test scores did not significantly improve achievement prediction. Exploratory factor analysis yielded a general ability factor (comprising the four IQ subtests, Digit Span, VMI, reading, and math), five factors made up solely of subtests from single measures (Wisconsin Card Sorting Test, Stroop Color and Word Test, Gordon Diagnostic System, California Verbal Learning Test, and ADHD ratings), a factor consisting of Grooved Pegboard Test and Coding, and a factor consisting of Symbol Search and Animal Naming Test.     

A correlational analysis between the PPVT-R and Woodcock-Johnson achievement cluster scores for nonreferred regular education and learning disabled students

Both forms of the PPVT-R, along with the reading, mathematics, and written-language subtests of the Woodcock-Johnson Psycho-Educational Test Battery were administered concurrently and in counterbalanced order to 28 nonreferred regular education and learning disabled students. With the exception of correlations between form M and the reading and written-language subtests for the LD group, values did not reach significance. Alternate form reliability coefficients for the RE and LD groups were .70 and .65, respectively. Mean standard scores for forms L and M were comparable for the RE group, but form L yielded a significantly higher score than M for the LD population.     

The relationship between self reports of college experiences and achievement test scores

This study evaluated the feasibility of using students' self reports of the academic development and college experiences as proxies and policy indicators for a national assessment of undergraduate education. Results indicated that self reports of academic development should be used with care as proxies for a national test. Particularly important are issues of content overlap and differences in the measurement methods. Results from the second part of this study supported using self reports of college experiences as policy indicators to improve undergraduate education.Paper presented at the annual forum of the Association for Institutional Research, New Orleans, May 1995.     

An operational definition of learning disabilities (cognitive domain) using WISC full scale IQ and peabody individual achievement test scores

An operational index of discrepancy to assist in identifying learning disabilities (LD) in the cognitive domain was derived using the Full Scale IQ, Wechsler Intelligence Scale for Children (Wechsler, 1949, and relevant subtest scores on the Peabody Individual Achievement Test (PIAT) (Dunn and Markwardt, 1970. The index was applied to all legally identified LD children (N = 60) of a Michigan county who were in the LD program (1% of the total elementary school population of 6000 children). Of the 50 males and 10 females (mean age: 9 years 2 months; mean IQ: 91), the index identified 74% and 30% respectively as may be LD in the cognitive domain. This comprised 67% of the 60 children, or 2/3 of 1 % of the total elementary school population. Of the 67% may be LD children, 93% had discrepancy low PIAT subtest scores in Reading Recognition, 88% in Reading Comprehension, 83% in Spelling, and 52% in Arithmetic. Considerable caution should be exercised when classifying children, especially females, as LD.     

The relationships between first name desirability and school readiness,IQ, and school achievement

The relationships between first name desirability and school readiness, IQ, and school achievement were explored using 1,727 elementary school children. Ratings of the desirability of first names were completed by 2,212 boys and girls in elementary and secondary schools. School readiness, IQ, and achievement variables showed small, but significant, correlations with first name desirability for girls; boys also showed a first name effect, but the magnitude was less. Most correlations remained significant even when the effects of parental education and ethnicity were partialled out. First name desirability was discussed as a specific case of stereotyping.     

Correlations between WISC-R subtests and verbal,performance, and full scale IQ scores for minority group children

The relationship between WISC-R subtest scores and Verbal, Performance, and Full Scale IQs was investigated for a sample comprised of rural Appalachian children. The sample was comprised of both white and black children who might be described as culturally different by virtue of low family income and residence in the mountainous areas of Virginia and North Carolina. Data analysis consisted of computing product-moment correlations (rs) between each of the ten subtests and the Verbal, Performance, and Full Scale IQs. Correlations between individual subtests and the FS IQ ranged from.49 through.63, but none of the differences between these rs were large enough to attain significance. Correlations between the verbal subtests and Verbal IQ ranged from.64 for Comprehension up to.78 for Vocabulary. For the performance subtest, the rs ranged from.54 between Coding and the Performance IQ up to.72 for Object Assembly.     

Effects of simple and regressed discrepancy models and cutoffs on severe discrepancy determination

Concern over the growing number of students identified as learning disabled has led school districts to examine the criteria for determination and the means by which they are operationalized. Two frequently used methods for determining a severe discrepancy between ability and achievement, a key criterion in LD determination, were applied to a sample of 344 students to determine how a change in method might influence the rates and characteristics of students meeting this criterion. The results indicate an increase in numbers when a regression method is used over a simple difference score method. When the change proposed included moving to a more severe cutoff score, the pattern reversed and a 20% decrease was observed. Although IQ correlated with the discrepancies when the simple difference score method was used, no correlation was observed when regression was employed, indicating that regression may be a more equitable method for calculating severe discrepancies. Neither method resulted in disproportionate racial representation among those meeting the severe discrepancy criterion.     

The influence of supplementary subtests on WISC IQ scores for high achieving students

The validity of Wechsler's (1949) comments concerning the addition of the supplementary WISC subtests was investigated for a sample of 20 fifth-grade students. The study was designed like that of Engin (1974) which investigated whether or not the addition of one or both of the supplementary WISC sub-tests, Digit Span and Mazes, materially affected the obtained IQs of high achieving fifth-grade subjects. All 12 subtests of the WISC were individually administered to the students, and IQs were then calculated in such a manner that specific comparisons could be made. These comparisons were between verbal, Performance and Full Scale IQs composed of the maximum number of subtests, and verbal, Performance, and Full Scale IQs exclusive of Digit Span, Mazes, or both subtests. T-tests for correlated means were employed and revealed highly significant differences. The addition of Digit Span and Mazes in the WISC battery served to depress the verbal, Performance and Full Scale IQs of the high achieving students. The study serves to validate the previous investigation by Engin (1974).