Fagan, Stephen; Gençay, Ramazan (2010), An introduction to textual econometrics, у Ullah, Aman; Giles, David E. A. (ред.), Handbook of Empirical Economics and Finance, CRC Press, с. 133—153, ISBN9781420070361. P. 139: «For example, in the Brown Corpus, consisting of over one million words, half of the word volume consists of repeated uses of only 135 words.»
