The relationship between vocabulary size, lexical diversity, lexical density and efl writing scores: A cross-sectional study

Vocabulary is an important aspect of language learning. Many studies were carried on vocabulary, vocabulary knowledge, vocabulary instruction, vocabulary learning and since 1990s the focus of the studies have shifted on the effects of vocabulary on second language (L2) learning. For Nation (2000) knowing a word includes form, meaning and use. The role of vocabulary knowledge in receptive and productive L2 skills cannot be ignored as it is used in predicting the learners' competence. It is obvious that this would affect L2 learners in expressing their thoughts through productive skills. The aim of the study is to find out the vocabulary size, lexical density and lexical diversity in argumentative essays of Turkish ELT students and to compare these with their writing scores. It is assumed that high vocabulary size, lexical density, and lexical diversity may lead to higher scores. The data, including 309 argumentative essays written by 165 first year and 144 fourth year students, were collected from Anadolu University ELT Department. In order to analyze the data and find answers to the research questions the LFP was used to obtain an estimate productive vocabulary size of the students, the vocd-D was used for lexical diversity of the essays, and the lexical density formula was used. According to the results, among other variables, only lexical diversity was found to have a significant correlation with 1st year students' essay scores and it significantly explained 7.8% of the 1st year essay scores. For the 4th year essays, no significant effect of the variables was found. Moreover, the results also demonstrated that while the variables accounted for 8.7% of the vocabulary scores in the 1st year essays, they did not yield a significant explanation for the 4th year essays vocabulary scores. Therefore, considering the results of the study, it can be concluded that lexical features are not the only factors effecting writing scores. Key Words: Vocabulary size, Lexical diversity, Lexical density, EFL writing, Turkish ELT students.