9Hinchcliffe R. Prevalence of the commoner ear, nose, and throat conditions in the adult rural population of Great Britain. A study by direct examination of two random samples. Br J Prey Soc Med, 1961, 15: 128-140.
10Leske MC. Prevalence estimates of communicative disorders in the U.S. Speech disorders. ASHA, 1981,23 : 217-225.