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BELL SYSTEM TECHNICAL JOURNAL 



Variation Over Longer Periods 



A comparison of data obtained at the New York Fair during a 

 period early in the summer and another period early in the fall is 

 given in Table 12. This table gives the difference in mean hearing 

 loss for the two periods for the various age and sex groups. A positive 

 difference indicates greater hearing loss in the later period. 



TABLE 12 



Difference Between Mean Hearing Losses Determined During Two 

 Different Periods 



The average difference is rather small, and may be taken to indicate 

 good stability on the part of the test equipment and lack of any pro- 

 nounced seasonal trends in hearing over this interval. 



Distribution of Hearing Acuity in the United 

 States Population 



The tests at the two Fairs constitute a large cross section of the 

 United States population. It is not a representative cross section in 

 certain respects, the most important of which are described below. 

 It is believed that by taking into consideration the limitations men- 

 tioned below an estimate of the distribution of hearing acuity in the 

 United States population can be obtained which is sufficiently accurate 

 for most practical purposes. 



The two Fairs taken together probably represent a good geographical 

 cross section of the country, except that areas near the Fairs were too 

 heavily represented. However, since no pronounced differences in 

 hearing were found for those living near the Fairs, the geographical 

 sampling may be regarded as fairly satisfactory. Although it is quite 



