Christine A Dollaghan1. 1. Department of Communication Sciences and Disorders, University of Texas, Dallas, TX, USA. dollaghan@utdallas.edu
Abstract
PURPOSE: To determine whether language scores at age 6 years suggest that specific language impairments (SLIs) distribute in a categorical or in a dimensional fashion. METHOD: A taxometric analysis of language scores from 601 six-year-old children who were free of neonatal risk factors was performed. From among 4 candidate indicators of SLI, 2 were eligible for the mean above minus below a cut (MAMBAC) procedure (Meehl & Yonce, 1994): number of different words (NDW) produced in a language sample and average percentage phonemes repeated correctly in 3- and 4-syllable nonwords (3-4 PPC). Graphs of these MAMBAC variables were inspected to determine whether they patterned in a manner suggesting the presence of a discrete category, having either a central peak or a steep curve peaking near the final interval. RESULTS: MAMBAC curves for NDW and 3-4 PPC did not suggest the presence of a taxon, and results did not vary during consistency checks in which MAMBAC parameters and cutoff values for language deficits were manipulated. CONCLUSIONS: Results suggest that for these measures, children with specific language deficits are those falling at the lower end of a continuous distribution of language skills rather than a qualitatively distinct group.
PURPOSE: To determine whether language scores at age 6 years suggest that specific language impairments (SLIs) distribute in a categorical or in a dimensional fashion. METHOD: A taxometric analysis of language scores from 601 six-year-old children who were free of neonatal risk factors was performed. From among 4 candidate indicators of SLI, 2 were eligible for the mean above minus below a cut (MAMBAC) procedure (Meehl & Yonce, 1994): number of different words (NDW) produced in a language sample and average percentage phonemes repeated correctly in 3- and 4-syllable nonwords (3-4 PPC). Graphs of these MAMBAC variables were inspected to determine whether they patterned in a manner suggesting the presence of a discrete category, having either a central peak or a steep curve peaking near the final interval. RESULTS: MAMBAC curves for NDW and 3-4 PPC did not suggest the presence of a taxon, and results did not vary during consistency checks in which MAMBAC parameters and cutoff values for language deficits were manipulated. CONCLUSIONS: Results suggest that for these measures, children with specific language deficits are those falling at the lower end of a continuous distribution of language skills rather than a qualitatively distinct group.
Authors: Pía Villanueva; Ron Nudel; Alexander Hoischen; María Angélica Fernández; Nuala H Simpson; Christian Gilissen; Rose H Reader; Lillian Jara; María Magdalena Echeverry; Maria Magdalena Echeverry; Clyde Francks; Gillian Baird; Gina Conti-Ramsden; Anne O'Hare; Patrick F Bolton; Elizabeth R Hennessy; Hernán Palomino; Luis Carvajal-Carmona; Joris A Veltman; Jean-Baptiste Cazier; Zulema De Barbieri; Simon E Fisher; Dianne F Newbury Journal: PLoS Genet Date: 2015-03-17 Impact factor: 5.917