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Fletcher, S.G. Diagnosing Speech Disorders from Cleft Palate. New York: Grune & Stratton, 1978.

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Kummer, A.W. Chapter 14, “Nasometry” in: Cleft Palate and Craniofacial Anomalies: Effects on Speech and Resonance, Second Edition. New York: Thomson Delmar Learning, 2008.