Jack M. Fletcher

Why IQ is not a covariate in cognitive studies of neurodevelopmental disorders

IQ scores are volatile indices of global functional outcome, the final common path of an individuals genes, biology, cognition, education, and experiences. In studying neurocognitive outcomes in children with neurodevelopmental disorders, it is commonly assumed that IQ can and should be partialed out of statistical relations or used as a covariate for specific measures of cognitive outcome. We propose that it is misguided and generally unjustified to attempt to control for IQ differences by matching procedures or, more commonly, by using IQ scores as covariates. We offer logical, statistical, and methodological arguments, with examples from three neurodevelopmental disorders (spina bifida meningomyelocele, learning disabilities, and attention deficit hyperactivity disorder) that: (1) a historical reification of general intelligence, g, as a causal construct that measures aptitude and potential rather than achievement and performance has fostered the idea that IQ has special status and that in studying neurocognitive function in neurodevelopmental disorders; (2) IQ does not meet the requirements for a covariate; and (3) using IQ as a matching variable or covariate has produced overcorrected, anomalous, and counterintuitive findings about neurocognitive function.

Form effects on the estimation of students' oral reading fluency using DIBELS.

This study examined the effects of passage and presentation order on progress monitoring assessments of oral reading fluency in 134 second grade students. The students were randomly assigned to read six one-minute passages in one of six fixed orders over a seven week period. The passages had been developed to be comparable based on readability formulas. Estimates of oral reading fluency varied across the six stories (67.9 to 93.9), but not as a function of presentation order. These passage effects altered the shape of growth trajectories and affected estimates of linear growth rates, but were shown to be removed when forms were equated. Explicit equating is essential to the development of equivalent forms, which can vary in difficulty despite high correlations across forms and apparent equivalence through readability indices.

Intensive Intervention for Students with Mathematics Disabilities: Seven Principles of Effective Practice

The focus of this article is intervention for third-grade students with serious mathematics deficits at third grade. In third grade, such deficits are clearly established, and identification of mathematics disabilities typically begins. We provide background information on two aspects of mathematical cognition that present major challenges for students in the primary grades: number combinations and story problems. We then focus on seven principles of effective intervention. First, we describe a validated, intensive remedial intervention for number combinations and another for story problems. Then, we use these interventions to illustrate the first six principles for designing intensive tutoring protocols for students with mathematics disabilities. Next, using the same validated interventions, we report the percentage of students whose learning outcomes were inadequate despite the overall efficacy of the interventions and explain how ongoing progress monitoring represents a seventh, and perhaps the most essential, principle of intensive intervention. We conclude by identifying issues and directions for future research in the primary and later grades.

Validity of Alternative Approaches for the Identification of Learning Disabilities Operationalizing Unexpected Underachievement

This article reviews the validity of models based on (a) aptitude—achievement discrepancies, (b) low achievement, (c) intraindividual differences, and (d) response to instruction for the classification and identification of learning disabilities (LD). Models based on aptitude—achievement discrepancies and intraindividual differences showed little evidence of discriminant validity. Low achievement models had stronger discriminant validity but do not adequately assess the most significant component of the LD construct, unexpected underachievement. All three of these status models have limited reliability because of their reliance on a measurement at a single time point. Models that incorporate response to instruction have stronger reliability and validity but cannot represent the sole criterion for LD identification. Hybrid models combining low achievement and response to instruction most clearly capture the LD construct and have the most direct relation to instruction. The assessment of students for LD must reflect a stronger underlying classification that takes into account relations with other developmental disorders as well as the reliability and validity of the underlying classification and resultant identification system.

Dyslexia: The evolution of a scientific concept.

In the past 25 years, scientific understanding of dyslexia and other learning disabilities has seen rapid progress in domains involving definition and classification, neuropsychological correlates, neurobiological factors, and intervention. I discuss this progress, emphasizing the central organizing influence of research and theory on basic academic skills on identification and sampling issues. I also emphasize how neuropsychological approaches to dyslexia have evolved and the importance of an interdisciplinary perspective for understanding dyslexia.

Altering the brain circuits for reading through intervention: a magnetic source imaging study.

Intervention-related changes in spatiotemporal profiles of regional brain activation were examined by whole-head magnetoencephalography in 15 children with severe reading difficulties who had failed to show adequate progress to quality reading instruction during Grade 1. Intensive intervention initially focused on phonological decoding skills (for 8 weeks) and, during the subsequent 8 weeks, on rapid word recognition ability. Clinically significant improvement in reading skills was noted in 8 children who showed normalizing changes in their spatiotemporal profiles of regional brain activity (increased duration of activity in the left temporoparietal region and a shift in the relative timing of activity in temporoparietal and inferior frontal regions). Seven children who demonstrated compensatory changes in brain activity (increased duration of activity in the right temporoparietal region and frontal areas, bilaterally) did not show adequate response to intervention. Nonimpaired readers did not show systematic changes in brain activity across visits.

Remediating Computational Deficits at Third Grade: A Randomized Field Trial.

Abstract The major purposes of this study were to assess the efficacy of tutoring to remediate 3rd-grade computational deficits and to explore whether remediation is differentially efficacious depending on whether students experience mathematics difficulty alone or concomitantly with reading difficulty. At 2 sites, 127 students were stratified on mathematics difficulty status and randomly assigned to 4 conditions: word recognition (control) tutoring or 1 of 3 computation tutoring conditions: fact retrieval, procedural computation and computational estimation, and combined (fact retrieval + procedural computation and computational estimation). Results revealed that fact retrieval tutoring enhanced fact retrieval skill, and procedural computation and computational estimation tutoring (whether in isolation or combined with fact retrieval tutoring) enhanced computational estimation skill. Remediation was not differentially efficacious as a function of students mathematics difficulty status.

Characteristics of a spina bifida population including North American Caucasian and Hispanic individuals.

BACKGROUNDnMeningomyelocele (MM) is a common human birth defect. MM is a disorder of neural development caused by contributions from genes and environmental factors that result in the NTD and lead to a spectrum of physical and neurocognitive phenotypes.nnnMETHODSnA multidisciplinary approach has been taken to develop a comprehensive understanding of MM through collaborative efforts from investigators specializing in genetics, development, brain imaging, and neurocognitive outcome. Patients have been recruited from five different sites: Houston and the Texas-Mexico border area; Toronto, Canada; Los Angeles, California; and Lexington, Kentucky. Genetic risk factors for MM have been assessed by genotyping and association testing using the transmission disequilibrium test.nnnRESULTSnA total of 509 affected child/parent trios and 309 affected child/parent duos have been enrolled to date for genetic association studies. Subsets of the patients have also been enrolled for studies assessing development, brain imaging, and neurocognitive outcomes. The study recruited two major ethnic groups, with 45.9% Hispanics of Mexican descent and 36.2% North American Caucasians of European descent. The remaining patients are African-American, South and Central American, Native American, and Asian. Studies of this group of patients have already discovered distinct corpus callosum morphology and neurocognitive deficits that associate with MM. We have identified maternal MTHFR 667T allele as a risk factor for MM. In addition, we also found that several genes for glucose transport and metabolism are potential risk factors for MM.nnnCONCLUSIONSnThe enrolled patient population provides a valuable resource for elucidating the disease characteristics and mechanisms for MM development.

Patterns of cognitive strengths and weaknesses: Identification rates, agreement, and validity for learning disabilities identification.

Few empirical investigations have evaluated learning disabilities (LD) identification methods based on a pattern of cognitive strengths and weaknesses (PSW). This study investigated the reliability and validity of two proposed PSW methods: the concordance/discordance method (C/DM) and cross battery assessment (XBA) method. Cognitive assessment data for 139 adolescents demonstrating inadequate response to intervention was utilized to empirically classify participants as meeting or not meeting PSW LD identification criteria using the two approaches, permitting an analysis of: (a) LD identification rates, (b) agreement between methods, and (c) external validity. LD identification rates varied between the 2 methods depending upon the cut point for low achievement, with low agreement for LD identification decisions. Comparisons of groups that met and did not meet LD identification criteria on external academic variables were largely null, raising questions of external validity. This study found low agreement and little evidence of validity for LD identification decisions based on PSW methods. An alternative may be to use multiple measures of academic achievement to guide intervention.

Association of folate receptor (FOLR1, FOLR2, FOLR3) and reduced folate carrier (SLC19A1) genes with meningomyelocele.

BACKGROUNDnMeningomyelocele (MM) results from lack of closure of the neural tube during embryologic development. Periconceptional folic acid supplementation is a modifier of MM risk in humans, leading toan interest in the folate transport genes as potential candidates for association to MM.nnnMETHODSnThis study used the SNPlex Genotyping (ABI, Foster City, CA) platform to genotype 20 single polymorphic variants across the folate receptor genes (FOLR1, FOLR2, FOLR3) and the folate carrier gene (SLC19A1) to assess their association to MM. The study population included 329 trio and 281 duo families. Only cases with MM were included. Genetic association was assessed using the transmission disequilibrium test in PLINK.nnnRESULTSnA variant in the FOLR2 gene (rs13908), three linked variants in the FOLR3 gene (rs7925545, rs7926875, rs7926987), and two variants in the SLC19A1 gene (rs1888530 and rs3788200) were statistically significant for association to MM in our population.nnnCONCLUSIONnThis study involved the analyses of selected single nucleotide polymorphisms across the folate receptor genes and the folate carrier gene in a large population sample. It provided evidence that the rare alleles of specific single nucleotide polymorphisms within these genes appear to be statistically significant for association to MM in the patient population that was tested.