RESULTS OF THE WORLD'S FAIR HEARING TESTS 



549 



cycles which results when the number of cases of hearing loss over 

 42 db is tripled. Eliminating all cases over 42 db would produce 

 about half as much shift in the opposite direction. However, the form 

 of the distribution curves for large values of hearing loss may be 

 substantially in error. 



Hearing losses at 3520 and 7040 cycles are much more common, 

 but are not likely to be noticed except when accompanied by a loss 

 at a lower frequency. Consequently, the biasing effect of a selective 

 process based on awareness of hearing loss is less pronounced at these 

 frequencies. 



Right and Left Ears 



The physical arrangements at the Fairs made it awkward for a 

 right-handed person to test his right ear. As a result, about 80 per 

 cent of the recorded tests were for the left ear. No appreciable differ- 

 ence was found between the test results for right and left ears. How- 

 ever, this may be taken as only a rough indication of equality between 

 the ears, in view of the differences in test conditions for the two ears. 



Time of Day 



Data from each Fair were studied to determine whether there was 

 any significant variation in hearing with time of day. Table 11, 

 which gives values of mean hearing loss covering a period of about 

 two weeks at the San Francisco Fair is typical. 



TABLE 11 

 Variation of Mean Hearing Loss with Time of Day 



The figures given are averages of several age groups. An apparent 

 slight trend to poorer hearing in the afternoon is probably not sig- 

 nificant, because detailed study of this and other data showed that 

 this trend was not consistent. It was concluded that there were no 

 trends of hearing acuity with time of day in any age group of sufficient 

 magnitude to be revealed by the survey. 



