In tests for higher level students, such as those taking the IELTS examination, lexical range in texts includes sub-technical words, which are seen as “academic vocabulary” by Marton (1976: 92). Cowan (1974: 391) defines these sub-technical words as “context independent words which occur with high frequency across disciplines”. Hence, IELTS reading tests do not simply measure candidates’ lexical knowledge, but how they identify meanings of difficult vocabulary within the context. In other words, test takers are not just required to recall the meaning of learned vocabulary but also to infer meaning from unknown ones as a means of facilitating reading comprehension.