How Specific Are Learning Disabilities?

Abstract

Despite historical emphasis on "specific" learning disabilities (SLDs), academic skills are strongly correlated across the curriculum. Thus, one can ask how specific SLDs truly are. To answer this question, we used bifactor models to identify variance shared across academic domains (academic g), as well as variance unique to reading, mathematics, and writing. Participants were 686 children ages 8 to 16. Although the sample was overselected for learning disabilities, we intentionally included children across the full range of individual differences in this study in response to growing recognition that a dimensional, quantitative view of SLD is more accurate than a categorical view. Confirmatory factor analysis identified five academic domains (basic reading, reading comprehension, basic math, math problem-solving, and written expression); spelling clustered with basic reading and not writing. In the bifactor model, all measures loaded significantly on academic g. Basic reading and mathematics maintained variance distinct from academic g, consistent with the notion of SLDs in these domains. Writing did not maintain specific variance apart from academic g, and evidence for reading comprehension-specific variance was mixed. Academic g was strongly correlated with cognitive g (r = .72) but not identical to it. Implications for SLD diagnosis are discussed.

Keywords: mathematics; reading; writing.

Figure 1. Correlated Factors Model – 5 Factors (Model 2 in Table 4).

Note. Model fit: X²(125)=401.08, p<.001, CFI = .96, RMSEA=.057 (90% CI=.051-.063), SRMR=.039, BIC=64800.52, AIC=64510.54, *p < .001 Abbreviations PIAT: Peabody Individual Achievement Test Reading TLWRT: Time Limited Word Recognition Test TOWRE: Test of Word Reading Efficiency GORT-3: Gray Oral Read ing Test—Third Edition WRAT-R: Wide Range Achievement Test—Revised ORI Reading Quest: Qualitative Reading Inventory – Reading Questions WJ-III: Woodcock-Johnson Tests of Achievement—Third Edition WIAT-III: Wechsler Individual Achievement Test – Third Edition TOWL-4: Test of Written Language – Fourth Edition Pass Comp: Passage Comprehension Applied Prob: Applied Problems Comp: Composition

Figure 2. Bifactar Madel (Madel 4 in Table 4)

Note. Model fit: X²(117)=382.22, p<.001, CFI=.96, RMSEA=.057 (90% CI=.051-.064), SRMR = .040, BIC=64833.90, AIC=64507.68, *p < .001 Abbreviations PIAT: Peabody Individual Achievement Test Reading TLWRT: Time Limited Word Recognition Test TOWRE: Test of Word Reading Efficiency GORT-3: Gray Oral Reading Test—Third Edition WRAT-R: Wide Range Achievement Test—Revised QRI Reading Quest: Qualitative Reading Inventory – Reading Questions WJ-III: Woodcock-Johnson Tests of Achievement—Third Edition WIAT-III: Wechsler Individual Achievement Test – Third Edition TOWL-4: Test of Written Language – Fourth Edition Pass Comp: Passage Comprehension Applied Prob: Applied Problems Comp: Composition