 In combination with this corpus evidence, researchers have monitored a range of classroom-based sources, including wordlists from leading coursebooks, readers’ wordlists and the content of vocabulary skills books.They have also referred to the Vocabulary Lists for the (KET) and Preliminary English Test (PET) examinations, which have been in use since 1994 and have been regularly updated to reflect language change and patterns of use.Finally, even though it was published thirty years ago, the Cambridge English Lexicon  by Roland Hindmarsh proved invaluable as a checking source, where the language has not evolved over time.