American Speech-Language-Hearing Association

Incidence and Prevalence of Speech, Voice, and Language Disorders in Adults in the United States: 2008 Edition

Effective communication skills are central to a successful life for all Americans. Communication disorders greatly affect education, employment, and the well-being of many Americans (1). Due to an apparent paucity of published data and peer-reviewed survey studies, it is difficult to assess the aggregate number of individuals in the U.S. who have speech, voice, and/or language disorders.

Speech Disorders

A speech disorder is an impairment of the articulation of speech sounds, fluency, and/or voice (2).

Fluency Disorders

A fluency disorder is an interruption in the flow of speaking characterized by atypical rate, rhythm, and repetitions in sounds, syllables, words, and phrases. This may be accompanied by excessive tension, struggle behavior, and secondary mannerisms (2).

  • Approximately 1% of the general population stutters (3, 4).
  • Developmental stuttering, characterized by sporadic repetitions, prolongations of phonemes or syllables, or both, typically becomes manifest between two and four years of age (5).
  • Developmental stuttering is the most common form of stuttering and includes all cases with gradual onset in childhood that are not the result of acquired brain damage. Persistent developmental stuttering is developmental stuttering that has not undergone spontaneous remission or reduction due to speech treatment (6).
  • The predisposition to stutter appears to be genetic, but this is not viewed as the only cause of the disorder (7).

Motor Speech Disorders

Motor speech disorders are impairments of speech arising from damage to the central or peripheral nervous system. The prevalence of neurogenic communication disorders (impairment due to brain damage) is high, and the figures are likely to increase within several populations, among which is the elderly in need of communication services (8). The diseases noted below often lead to motor speech disorders.

Parkinson's Disease

  • The causes of Parkinson's Disease (PD), the second most common neurodegenerative disorder, are still largely unknown (9). The prevalence of PD in industrialized countries is estimated at 0.3% of the general population, and about 1% of the population older than 60 years. People of all ethnic origins can be affected, and men are slightly more prone to the disorder (10, 11).
  • Although motor features define PD, various non-motor features typically are seen, including autonomic dysfunction, cognitive and psychiatric changes, sensory symptoms, and sleep disturbances (10).
  • Speech and voice disorders are very common among individuals suffering from PD (12). One study estimates that 89% of individuals with PD have a speech or voice disorder. Despite the high incidence of the disorders, studies suggest that only 3%-4% of individuals with PD receive speech treatment (13).

Huntington's Disease

  • Huntington's Disease (HD) is a fatal, genetically based brain disorder in which there is progressive neurodegeneration leading to motor, cognitive and psychiatric symptoms (14). HD affects 5 out of 100,000 people and symptoms usually occur at the age of late 40s (15).
  • Age onset varies markedly, typically occurring between the ages of 35 and 50. The course is relentlessly progressive, with death usually occurring 15-20 years after disease onset (16).
  • Cognitive abnormalities usually begin at about the same time as movement abnormalities. Cognitive speed and efficiency are relatively impaired (16). Cognitive deficits typically include an overall slowing of thinking processes, difficulty initiating and maintaining conversation, and an inability to learn new and/or abstract information (17).
  • Motor speech deficits are both the most prominent and the most clearly described contributor to changes in communication. Individuals present an unpredictable speech pattern that may severely compromise clarity of speech (17).

Amyotrophic Lateral Sclerosis

  • Amyotrophic Lateral Sclerosis (ALS) is a progressive degenerative disease that affects those in middle-age. The etiology of ALS is not entirely understood. Only 5%-10% of cases are familial. Men are affected 1½ to 2 times more commonly that women. The average duration of survival is 3 to 5 years. Disease prevalence ranges from 0.5 to 3 in 100,000, with a few areas of higher prevalence (18).
  • Oropharyngeal dysphagia is highly prevalent in patients with ALS (19).
  • Strained, strangled, and tremulous vocal qualities are typically seen in patients with ALS (20).
  • Because the disease usually doesn't affect cognitive abilities, patients are aware of their progressive loss of function and may become anxious and depressed (21).

Traumatic Brain Injury

Please refer to the report Communication Facts, Special Populations: Traumatic Brain Injury.

Voice Disorders

  • Voice disorders are characterized by the abnormal production and/or absence of vocal quality, pitch, loudness, resonance, and/or duration, given an individual's age and/or sex (2).
  • Epidemiologic studies of the prevalence and risk factors of voice disorders in the general adult population are rare (22). According to conservative estimates, approximately 28 million workers in the U.S. experience daily voice problems (23); a second study estimates that 5% to 10% of the U.S. workforce would be classified as heavy occupational voice users (24).
  • According to one study, the lifetime prevalence of a voice disorder is almost 30%. Disorders also adversely impact job performance and attendance (22).
  • Teachers, as compared with non-teachers, have missed more workdays because of voice problems and were more likely to consider changing occupations because of their voice (25). Estimates based on empirical data suggest that, considering only lost work days and treatment expenses, the societal cost of voice problems in teachers alone may be approximately $2.5 billion (23).
  • Functional dysphonia refers to a loss of voice in the absence of identifiable neurological or structural pathology. Functional dysphonia, which may account for more than 10% of cases referred to multidisciplinary voice clinics, occurs mainly in women and commonly follows upper respiratory infection symptoms (26).
  • Spasmodic dysphonia is a disorder characterized by involuntary movements of one or more muscles of the larynx or voice box. The first signs of spasmodic dysphonia are most often found in individuals between 30 and 50 years old. More women appear to be affected by spasmodic dysphonia than men (27).

Language Disorders

  • A language disorder is the impaired comprehension and/or use of spoken, written, and/or other symbol systems (2).
  • About one million persons in the United States have aphasia (partial or complete impairment of language comprehension and expression caused by brain damage, most often from stroke) (28).
  • It is estimated that approximately 80,000 individuals acquire aphasia each year (28).
  • Language disorders are also found in adults who have failed to develop normal language because of childhood autism, hearing impairment, or other developmental or acquired disorders of brain development (28).


  1. National Institute on Deafness and Other Communication Disorders. Strategic plan: 2006-2008. <Accessed May 8, 2007, [PDF]>.
  2. ASHA Ad Hoc Committee on Service Delivery in the Schools. (1993, March). Definitions of communication disorders and variations. Asha, 35 (Suppl. 10), 40-41.
  3. Packman, A., & Onslow, M. (2002, August 31). Searching for the cause of stuttering. Lancet, 360 (9334): 655-656.
  4. Sommer, M., et al. (2002, August 3). Disconnection of speech-relevant brain areas in persistent developmental stuttering. Lancet, 360 (9330): 380-384.
  5. Sandak, R., & Fiez, J.A. (2000, August 5). Stuttering: a view from neuroimaging. Lancet, 356 (9228): 445-456.
  6. Kumar, A., & Balan, S. (2007, January-February). Fluoxetine for persistent developmental stuttering. Clinical Neuropharmacology, 30 (1): 58-59.
  7. Altholz, S., & Golensky, M. (2004, August). Counseling, support, and advocacy for clients who stutter. Health & Social Work, 29 (3): 197-206.
  8. Herndon, C.M., Young, K., Herndon, A.D., et al. (2000, August). Parkinson's disease revisited. Journal of Neuroscience Nursing, 32 (4): 216:221.
  9. deLau, M., & Breteler, M.M. (2006, June). Epidemiology of Parkinson's Disease. Lancet Neurology, 5 (6): 525-535.
  10. Samii, A., Nutt, J.G., & Ranson, B.R. (2004, May 29). Parkinson's disease. Lancet, 363 (9423): 1783-1793.
  11. Levine, C.B., Fahrbach, K.R., Siderowf, A.D., et al. (2003, June). Diagnosis and treatment of Parkinson's disease: a systematic review of the literature. Evidence Report/Technology Assessment number 57. (Prepared by Metaworks, Inc., under Contract No. 290-97-0016). AHRQ Publication No. 03-E040. Rockville, MD: Agency for Healthcare Research and Quality.
  12. Ramig, L.O., Fox, C., & Sapir, S. (2004, May). Parkinson's disease: speech and voice disorders and their treatment with the Lee Silverman Voice Treatment. Seminars in Speech and Language, 25 (2): 169-180.
  13. Trail, M., et al. (2005). Speech treatment for Parkinson's Disease. Neurorehabilitation, 20 (3): 205-221.
  14. Hannan, A.J. (2004, April). Huntington's disease: which drugs might help patients? IDrugs: the Investigational Drugs Journal, 7 (4): 351-358.
  15. Qin, Z., & Gu, Z. (2004 October). Huntingtin processing in pathogenesis of Huntington disease. Acta Pharmacologica Sinica, 25 (10): 1243-1249.
  16. Margolis, R.L., & Ross, C.A. (2003). Diagnosis of Huntington disease. Clinical Chemistry, 49 (10): 1726-1732.
  17. Klasner, E.R., & Yorkston, K.M. (2001, September). Linguistic and cognitive supplementation strategies as augmentative and alternative communication techniques in Huntington's disease: Case report. Augmentative and Alternative Communication, 17, 154-160.
  18. Khan, T.S., & Prayson, R.A. (2003, February). Pathologic quiz case: a 50 year-old man with progressive worsening of neurological symptoms. Archives of Pathology & Laboratory Medicine, 127, e113-e114.
  19. Kidney, D., Alexander, M., Corr, B., O'Toole, O., & Hardiman, O. (2004, September). Oropharyngeal dysphagia in amyotrophic lateral sclerosis: neurological and dysphagia specific rating scales. Amyotrophic Lateral Sclerosis and Other Motor Neuron Disorders, 5 (3): 15-153.
  20. Lundy, D.S., Roy, S., Xue, J.W., Casiano, R.R., & Jassir, D. (2004, March). Spastic/spasmodic vs. tremulous vocal quality: motor speech profile analysis. Journal of Voice, 18 (1): 146-152.
  21. National Institute of Neurological Disorders and Stroke. Amyotrophic lateral sclerosis fact sheet. <Accessed May 8, 2007,>.
  22. Roy, N., Merrill, R.N., Gray, S.D., & Smith, E.M. (2005, November). Voice disorders in the general population: Prevalence, risk factors, and occupational impact. Laryngoscope, 115 (11): 1988-1995.
  23. Verdolini, K., & Ramig, L.O. (2001). Review: occupational risks for voice problems. Logopedics, Phoniatrics, Vocology, 26 (1): 37-46.
  24. Roy, N., Weinrich, B., Gray, S.D., et al. (2003, June). Three treatments for teachers with voice disorders: A randomized clinical trial. Journal of Speech, Language, and Hearing Research, 46, 670-688.
  25. Roy, N., Merrill, R.N., Thibeault, S., Gray, S.D., & Smith, E.M. (2004, June). Voice disorders in teachers and the general population: effects on work performance, attendance, and future career choices. Journal of Speech, Language, Hearing Research, 47 (3): 542-551.
  26. Roy, N., & Bless, D.M. (2000, June). Personality traits and psychological factors in voice pathology: A foundation for future research. Journal of Speech, Language, and Hearing Research, 43, 737-748.
  27. National Institute on Deafness and Other Communication Disorders. Spasmodic dysphonia. <Accessed May 8, 2007,>.
  28. National Institute on Deafness and Other Communication Disorders. Aphasia. <Accessed May 8, 2007,>.


Compiled by Andrea Castrogiovanni * American Speech-Language-Hearing Association* 2200 Research Boulevard, Rockville, MD 20850 *

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