Date of Award

2023

Document Type

Open Access Thesis

Department

Public Health

First Advisor

Suzanne Adlof

Second Advisor

Marc Goodrich

Abstract

Purpose - Developmental language disorder (DLD) is a common yet underdiagnosed disorder centered on difficulties with oral language, and often associated with word reading and reading comprehension difficulties. Numerous studies have documented high rates of reading impairment in children with DLD, but the specific rates vary widely across studies. The purpose of this meta-analysis was to help provide accurate prognostic information about this disorder by determining the average proportion of participants with DLD who also had reading impairment, and to determine whether variability in the rate of reading impairment was significantly influenced by studies’ methodological features, including recruitment method, type of reading measure, age of participants, and nonverbal IQ criterion.

Methods - We searched the PsycINFO database for peer-reviewed research articles containing keywords related to DLD and dyslexia, resulting in a total of 310 studies. After screening these articles for our inclusion/exclusion criteria, 33 studies were coded and 49 rates were extracted for analysis. Multivariate meta-analysis models were run in the R statistics platform using a multi-level modeling framework with effect sizes nested within studies.We analyzed transformed values because the robust variance estimation did not support the analytic approach. the robust variance estimation method.

Results - The estimated average rate of reading impairment in children with DLD across a sample of 43 comorbidity rates was 55.6%. None of the methodological factors demonstrated a significant influence on reported comorbidity; however, statistical power was low for the moderator analyses due to small study numbers. Although not significant, the finding that caseload samples had a numerically higher average rate of co-occurrence (58.0%) than community samples (43.9%) was consistent with our hypotheses.

Discussion - The high average rate of reading impairment observed in children with DLD (56%) suggests that children with this disorder are likely to struggle with both oral language and written language skills and will likely require support in both domains. However, even though rates of co-occurring reading impairment were quite high, it’s important to note that the average estimated rate of dyslexia (word reading impairment) in children with DLD was 54.6% which contradicts suggestions that all children with DLD will exhibit decoding deficits. It’s important that studies consider this comorbidity when studying children with DLD to ensure an accurate reflection of the DLD profile. We encourage researchers, SLPs/educators, and other related professionals who work with these children to consider the impact that methodological decisions have on determining the co-occurrence of reading impairment in children with DLD.

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