Modelling and Assessing Vocabulary Knowledge: What is in a teacher's mind? Teacher ratings of EFL essays and different aspects of lexical richness

Introduction and overview The findings of the present chapter are a contribution to the discussion on the role of lexical richness within the construct of foreign language proficiency. The present study investigates to what extent teacher judgement of EFL essays can be predicted by measuring the lexical richness of these texts. Thirty-one essays from students on English for Academic Purposes (EAP) short courses were analysed with various measures of lexical richness ( D, Advanced Types, P-Lex, Guiraud's Index, Advanced Guiraud and Type-Token Ratio (TTR)). Four experienced EFL teachers rated the essays according to a set of band descriptors that was familiar to the teachers, and is also used in EAP exams. The raters were asked to judge the overall proficiency and a number of other linguistic aspects of the texts. Although the teachers did have different individual preferences in the detailed analysis of the essays, there was a highly significant correlation between them, especially on the overall score (rho >.9), which is an indication of reliable rating. Other studies on teacher ratings of oral texts (Richards and Malvern, 2000; Malvern and Richards, 2002; Malvern, Richards, Chipere, and Duran, 2004: 103) suggest that teacher rating is influenced by the use of advanced vocabulary or rare words. The present study confirms this for written texts as well. In line with our expectations this chapter shows that the measures based on the occurrence of infrequent words are most useful in predicting teacher judgement.