118 ILLINOIS ACADEMY OF SCIENCE 



TABLE II.— RELATION OF PERCENTAGE OF FAT TO AMOUNT 

 OF PRODUCTION— SEMI-OFFICIAL TEST 



Omitting the last class in which but a single record occurs 

 we find that cows which produce 320.59 pounds fat test, on 

 the average, 31.35 per cent fat, whereas those cows which pro- 

 duce 993.32 pounds fat test, on the average, 3.79 per cent, a 

 difference of but .44 of 1 per cent. This would seem to indi- 

 cate that the semi-official test is more uniform with respect to 

 percentage of fat both in low and in high production than the 

 seven-day test. 



Even more interesting and significant than the study of the 

 relation of these two tests with respect to fat percentage is 

 that of the correlation which exists between them. By using 

 the standard method for calculating the correlation coefficient 

 we find that the correlation which exists between seven-day 

 and semi-official fat production is .662 ±.011. This for many 

 purposes would be regarded as a high degree of correlation, but 

 it is not so regarded between two measurements of the same 

 thing, namely the productive ability of a given group of cows. 

 The correlation between seven-day semi-official milk produc- 

 tion is .658±.011, almost the same as the correlation found for 

 fat production. 



It would seem from these studies that the seven-day test is 

 not a very dependable criterion by which to judge semi-official 

 or yearly production. 



