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BELL SYSTEM TECHNICAL JOURNAL 



The differences shown suggest a relation between hearing acuity 

 and general personal appearance, although the evidence is not con- 

 clusive. In each of the ten comparisons given in the table, there is 

 an increase in hearing acuity in going from average to above average 

 and in nine out of ten there is an increase in going from below average 

 to above average. Personal appearance is somewhat related to 

 economic status and intelligence. A more accurate index of these 

 might show a more striking relation with hearing acuity. 



Race 



The number of tests of negroes tabulated thus far is too small to 

 give a satisfactory picture of the hearing trends among them. How- 

 ever, there is no indication of substantial departure from the results 

 reported by Bunch and Raiford,^ who determined that the hearing of 

 negro men and women is similar to that of white women. 



Awareness of Hearing Impairment 



People whose hearing is impaired are often quite sensitive, and it 

 seems possible that some may have avoided the hearing test for this 

 reason. On the other hand, a person with impaired hearing might be 

 especially attracted by the opportunity to measure it. Whether the 

 data show too high or too low an incidence of hearing impairment 

 depends on which of these factors predominates. This is a possi- 

 bility for bias that is present in any survey where participation is 

 voluntary. No satisfactory method of evaluating it has been dis- 

 covered. However, the following discussion is intended to give some 

 idea of the magnitude of the error which may be involved. 



Since a person is scarcely aware of a hearing loss of less than 25 db, 

 it may be assumed that neither of these factors would affect the dis- 

 tributions below that value. For greater losses some effect may be 

 expected, gradually increasing so that above 40 db the possibility of a 

 substantial bias in the distributions must be considered. The shift 

 of the mean values of hearing loss is probably not very pronounced. 

 For example, Table 10 shows the shift in mean hearing loss at 1760 



TABLE 10 



^ C. C. Bunch and T. S. Raiford, "Race and Sex Variations in Auditory Acuity, 

 Arch, of Otolaryng., 13: 423-434 (1931). 



