In a recent DISCOVER Magazine post the author of its Gene Expression blog, Razib Khan, wrote a piece called “Higher Vocabulary ~Higher Income”. Exploring the correlation between intelligence and income, he used the statistical correlation between intelligence and vocabulary to show the correlation between vocabulary and income.
It must be added that the differences in vocabulary here are not differences learned in oral conversation. After grade 4 vocabulary growth is largely driven through literacy not speech. Because most of the difference in adult vocabulary is a result of reading, using vocabulary as a proxy for intelligence is an indirect way of pointing to the role of reading in intelligence. Advance the following video (“Reading Matters”) to 1:14 for a sequence on reading, vocabulary, and intelligence. After that it’s easier to understand what Dr. Louisa Moats means in the second video (“Academic Danger”).