Date of Award

Spring 1-1-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Psychology & Neuroscience

First Advisor

Erik G. Willcutt

Second Advisor

Richard K. Olson

Third Advisor

Soo Rhee

Fourth Advisor

Vijay Mittal

Fifth Advisor

Victoria Hand

Abstract

In the past, specific learning disorders in reading and mathematics have been conceptualized as distinct and content-specific disorders of learning. The procedure for diagnosing these disorders has varied in research and in clinical practice, with a wide range of achievement measures and diagnostic criteria being employed. The purpose of the current study was to improve classification procedures for learning disabilities by exploring the latent factor structure of reading and math achievement measures and by using latent profile analysis (LPA) to differentiate profiles of learners based on reading and math achievement scores. Using two complementary datasets that included children from the Colorado Learning Disabilities Research Center and the International Longitudinal Twin Study of Early Reading Development, latent factor analysis indicated that reading and math measures are correlated but separable into content-specific factors. In contrast, the LPA indicated that classes of individuals were separated only by the severity of their performance on both reading and math measures, rather than distinct profiles of specific reading or math weakness. Measures of academic functioning, neuropsychological, and psychosocial functioning differed significantly across the LPA-defined classes, providing important evidence of the external validity to the groups. In both studies, the class with the lowest performance on the reading and math achievement measures tended to also have the greatest difficulty with academic functioning, the lowest neuropsychological functioning, and the highest levels of symptoms related to externalizing behaviors. Taken together, our results suggest that although dimensional measures of reading and math achievement are differentiable on a conceptual and empirical level, individuals with academic difficulties tend to perform poorly in both domains, suggesting that learning disorders in reading and math are not distinct.

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