doi:10.1093/applin/amu007 The Effects of Vocabulary Breadth and Depth on

This study explored the relationship between two dimensions of vocabulary knowledge, that is, breadth of vocabulary (the number of words known) and depth of vocabulary (the richness of word knowledge), and their effects on different aspects of English reading in Chinese high school students learning English as a second language. Two hundred and forty-six Grade 8 students in China were administered measures of word reading, vocabulary breadth, vo-cabulary depth, and reading comprehension. Results showed that breadth and depth of vocabulary were moderately correlated. They both contributed to word reading, but breadth of vocabulary had a stronger effect than depth of vocabu-lary. When reading comprehension was the outcome measure, vocabulary breadth significantly predicted a multiple-choice reading comprehension meas-ure, which requires general understanding of the text, while vocabulary depth contributed to summary writing, a measure of deeper text processing. Discussion focuses on the important roles of different dimensions of vocabulary knowledge for different types of second language reading. According to the Lexical Quality Hypothesis (Perfetti 1985, 2007), skilled reading depends on high-quality lexical representations, and therefore vocabulary should be a powerful predictor of reading. Many empirical studies in both English as a first language (EL1) and English as a second language (ESL) have demonstrated that there is a close relationship between vocabulary knowledge and reading (e.g. Stahl and Fairbanks 1986; Qian 1999, 2002; Nation 2001; Beck et al. 2002). Although many studies have found a strong relationship between vocabulary and reading, they have often employed only a single measure of vocabulary and have not addressed the multidimensional nature of vocabulary knowledge (Kieffer and Lesaux 2008). It has been proposed that traditional measures of vocabulary assess mainly breadth of vocabulary, because although they do capture a sense of how many words are known, they do not indicate how well or how deeply those word