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BELL SYSTEM TECHNICAL JOURNAL 



Each observer's sheet (Table II) furnishes a value of syllable 



articulation (the percentage correctly observed), corresponding to a 



particular caller-observer pair and to 66 syllables or 198 speech sounds 



called. These values of syllable articulation are recorded in the form 



shown in Table III. The average of each column gives the average 



articulation for each observer. The averages of the rows give the 



callers' articulation. 



TABLE III 



£/29/28 



Apticulation Test Result Record 



When the articulation values are near 100 per cent or per cent, 

 then a group of values will not distribute itself symmetrically about 

 the arithmetic mean or average value. For the high values, this is 

 due to the fact that one cannot get a higher value than 100 per cent. 

 To some observers, the 100 per cent mark may be obtained very 

 easily and to others it may be obtained only with considerable effort. 

 This difference in difficulty cannot be registered in the percentages 

 obtained. A similar reason exists for the unsymmetrical grouping for 

 values near zero. Our experiments have shown that this grouping is 

 symmetrical in the range from 20 per cent to 80 per cent. For the 

 range from 80 per cent to 100 per cent, the average value is less than 

 the most frequent value, and for the range from per cent to 20 per 

 cent, the average value is greater than the most frequent value. 

 These differences are of the order of 1 or 2 per cent. From an 

 extensive series of tests, the averaging factor curve of Fig. 1 was 

 constructed which enables the data to be averaged, in a way, such 

 that the average value is approximately equal to the value which 

 would be most frequently observed in a large number of tests. To do 

 this, each observed articulation, based on 66 syllables, is converted 

 into an averaging factor by means of the above curve. These factors 

 are then averaged and the average value reconverted into average 



