A Cambridge english vocabulary says
The Cambridge Learner Corpus is a collection of over 44 million words of English, based upon evidence of language use by learners from all over the world and from
which
the English Vocabulary Profile has developed. The English Vocabulary Profile shows the most common words and phrases that learners of English need to know in British or American English. The meaning of each word or phrase in the wordlists has been assigned a level between A1 and B2 on the CEFR.
Is WHICH referring to "The Cambridge Learner Corpus", "evidence of language" or something else?