Differential lexical predictors of reading comprehension in fourth graders.

The mental lexicon plays a central role in reading comprehension (Perfetti & Stafura, 2014). It encompasses the number of lexical entries in spoken and written language (vocabulary breadth), the semantic quality of these entries (vocabulary depth), and the connection strength between lexical representations (semantic relatedness); as such, it serves as an output for the decoding process and as an input for comprehension processes. Although different aspects of the lexicon can be distinguished, research on the role of the mental lexicon in reading comprehension often does not take these individual aspects of the lexicon into account. The current study used a multicomponent approach to examine whether measures of spoken and written vocabulary breadth, vocabulary depth, and semantic relatedness were differentially predictive of individual differences in reading comprehension skills in fourth-grade students. The results indicated that, in addition to nonverbal reasoning, short-term memory, and word decoding, the four measures of lexical quality substantially added (30 %) to the proportion of explained variance of reading comprehension (adding up to a total proportion of 65 %). Moreover, each individual measure of lexical quality added significantly to the prediction of reading comprehension after all other measures were taken into account, with written lexical breadth and lexical depth showing the greatest increase in explained variance. It can thus be concluded that multiple components of lexical quality play a role in children's reading comprehension.