RESULTS OF THE WORLD'S FAIR HEARING TESTS 



539 



believed that this is due principally to the greater difficulty of the 

 younger children in understanding the test and writing their responses 

 on the test blank. 



TABLE 3 

 Standard Deviation of Hearing Loss in db 



Table 3 shows the standard deviations of the hearing losses for 

 single tests. They range in magnitude from 7 to 20 db, and tend to 

 increase with increasing age and tone frequency. An exception occurs 

 for the 440-cycle tone where the values are mostly larger than for the 

 880-cycle tone. Since previous surveys have not shown a tendency 

 for the standard deviation to increase below 880 cycles, it seems likely 

 that the present increase occurred because the 440-cycle tone was the 

 first one in the test, and initial unfamiliarity produced a greater 

 scattering of the results. Carelessness in holding the receiver snugly 

 against the ear would produce a similar scattering of results at this 

 frequency. 



The mean hearing losses and standard deviations for the older 

 groups for the two high-frequency tones would be somewhat larger 

 were it not for the restricted scale of the test. At 3520 cycles the 

 range from zero is only 46 db, and at 7040 cycles, only 33 db. In com- 

 puting means and standard deviations all results lying beyond the 

 range of the test were grouped one test step beyond the extreme value 

 included in the test. 



Distribution of Hearing Loss 



In addition to giving the trends in average hearing, the hearing test 

 scores afford a means of determining the frequency of occurrence of 

 different amounts of hearing loss. A convenient method of presenting 

 the occurrence rates of different degrees of deafness is by means of 

 curves or tables showing cumulative distributions. Table 4 shows 



