RESULTS OF THE WORLD'S FAIR HEARING TESTS 551 



possible that sections might be found in which hearing differed 

 markedly from the Fair values, it is unlikely that such areas would be 

 extensive enough to affect the overall result. 



With regard to economic status, intelligence, and amount of educa- 

 tion, the Fair groups were judged to be somewhat above average, and 

 probably representative of the upper two-thirds or three-quarters of 

 the population. If hearing is related to such factors, as seems prob- 

 able, the hearing of the population is not quite so good as indicated by 

 the Fair tests. 



The portion of the distribution curves relating to large hearing 

 losses at the three lower frequencies must be accepted with reservations 

 on account of the possible biasing effect of awareness of hearing im- 

 pairment, as discussed in the preceding section. However, the curves 

 should be reliable below about 35 db loss, and the curves for the two 

 highest frequencies should be reliable throughout the test range. 



The distribution of ages at the Fairs was quite different from that 

 in the population. The first step in allowing for that difference was 

 made by recombining the distributions of hearing loss for various age 

 and sex groups shown in Table 4, weighting each according to the size 

 of the group in the population. The resulting distributions are shown 

 in Fig. 5, and apply to the age range 10-59 years.'* 



In a similar manner, the figures in Table 5 for the incidence of 

 hearing loss of 25 db or more were weighted according to the size of 

 the groups and combined, leading to the values given in the first line 

 of Table 13, for the age range 10-59. This process can be extended 

 to include the whole age range as follows. It is assumed that the 

 incidence for ages under 10 is the same as in the 10-19 group. This 

 may not be strictly true, but is a sufficiently good approximation for 

 this purpose. For ages above 60 a minimum estimate was obtained 

 by assuming that the incidence of hearing loss is the same as in the 

 50-59 group, and a maximum estimate by assuming 100 per cent 

 incidence above age 60. The actual value may be expected to be 

 somewhere between these limits, which are shown in Table 13. 



Except for the reservations stated in the first four paragraphs of 

 this section, it is believed that the data of Figs. 3, 4, and 5 and Tables 

 2, 3, 4, 5, and 13 should apply fairly closely to the U. S. population as 

 a whole. They may also be applied to groups in the population who 

 are not specialized in regard to any factor related to hearing. It would 

 be unsafe to apply them to a group of very low or unusually high 

 economic status, college graduates, unskilled laborers, foreign groups, 



* Loc. cit. 



