How much vocabulary is needed to use a concordance?

Vocabulary load is a predictor of comprehension and a common concern in relation to learner use of concordances; however, vocabulary load figures for whole texts have limited relevance to learner use of concordances. This paper explores the average vocabulary load of the citations (or lines) in a concordance, reflecting how learners use concordances as reading or reference resources. Non-parametric tests are used to compare the vocabulary loads of citations from three authentic written corpora and a corpus of graded readers. The results indicate that citations from authentic corpora have an average vocabulary load of 4,000-5,000 word families, there are reliable differences in vocabulary load between citations from different corpora, and the magnitude of difference between citations from authentic corpora can be equivalent to the magnitude of difference between authentic corpora and graded reader corpora. The paper concludes with a discussion of the results in relation to language learner use of concordances.