↑ Beech, John R.; Harding, Leonora; Hilton-Jones, Diana (1993). Assessment in speech and language therapy. CUP Archive. p. 55. ISBN0415078822.CS1 maint: Multiple names: authors list (link)
↑ Labov, William (2003). "Some Sociolinguistic Principles". In Paulston, Christina Bratt; Tucker, G. Richard. Sociolinguistics: the essential readings. Wiley-Blackwell. pp. 234–250. ISBN0631227172.CS1 maint: Multiple names: editors list (link)
↑ Schultz, Tanja; Kirchhoff, Katrin (2008). Multilingual speech processing. Academic Press. p. 12. ISBN0120885018.CS1 maint: Multiple names: authors list (link)
