1. American Speech-Language-Hearing Association. (2007). Speech sound disorders: Articulation and phonological disorders.
www.asha.org/public/speech/disorders/SpeechSoundDisorders.
2. American Speech-Language-Hearing Association. (2008). Incidence and prevalence of communication disorders and hearing loss in children (2008 ed.).
www.asha.org/members/research/reports/children.