O’Leary, N. C., P. D. Murphy, S. J. Drinkwater, and D. H. Blackaby. “English Language Fluency and the Ethnic Wage Gap for Men in England and Wales”. Economic Issues, vol. 6, no. 1, Mar. 2001, pp. 21-32, https://mail.economicissues.org.uk/index.php/EI_OJS/article/view/69.