190 



Maine Agricultural Experiment Station. 1920. 



Observation of table I shows that there is a considerable 

 relation of milk secretion to age. The correlation coefficient as 

 deduced from these data is -(-0.4332+. 0108. The extreme 

 skewness of the data tends to reduce the size of the correlation 

 coefficient as compared to the true relationship which does exist. 

 In view of this fact only slight dependence can be placed in its 

 absolute value. However, since the true amount of relationship 

 would be increased rather than decreased were the skewness re- 

 moved, it follows that there is a distinctly significant association 

 of milk secretion to age. As our object is not the amount of the 

 correlation which exists between these variables age and milk 

 yield but is the form and equation to the curve which describes 

 the relation we need not pause longer on this phase of the sub- 

 ject. 



Proceeding to the calculations of the mean milk production 

 within the age groups as seen in table I we find the mean 365 

 day milk yields to be those shown in table 2. 



TABLE 2. 



Mean 365 Day Milk Yield of H olstein-Friesian Cows at 

 Different Ages. 







Age at Tesl 







Mean milk 









Age at Test 







Mean milk 















Yield 



















Yield 



1 yr. 



6 



mo. 



to 1 yr. 



11 



mo. 



12007 



8 



yr. 







mo. to 



8 



yr. 



5 



mo. 



19405 



2 yr. 







mo. 



to 2 yr. 



5 



mo. 



13774 



8 



yr. 



6 



mo. to 



8 



yr. 



11 



mo. 



18560 



2 yr. 



6 



mo. 



to 2 yr. 



11 



mo. 



14264 



9 



yr. 







mo. to 



9 



yr. 



5. 



mo. 



18414 



3 yr. 







mo. 



to 3 yr. 



5 



mo. 



15623 



9 



yr. 



6 



mo. to 



9 



yr. 



11 



mo. 



19654 



3 yr. 



6 



mo. 



to 3 yr. 



11 



mo. 



15860 



10 



yr. 







mo .to 



10 



yr. 



5 



mo. 



17292 



4 yr. 







mo. 



to 4 yr. 



5 



mo. 



16528 



10 



yr. 



6 



mo. to 



10 



yr. 



11 



mo. 



17500 



4 yr. 



6 



mo. 



to 4 yr. 



11 



mo. 



16972 



11 



yr. 







mo. to 



11 



yr. 



5 



mo. 



19833 



5 yr. 







mo. 



to 5 yr. 



5 



mo. 



17511 



11 



yr. 



6 



mo. to 



11 



yr. 



11 



mo. 



19833 



5 yr. 



6 



mo. 



to 5 yr. 



11 



mo. 



18178 



12 



yr. 







mo. to 



12 



yr. 



5 



mo. 



16000 



6 yr. 







mo. 



to 6 yr. 



5 



mo. 



18675 



12 



yr. 



6 



mo. to 



12 



yr. 



11 



mo. 



17000 



6 yr. 



6 



mo. 



to 6 yr. 



11 



mo. 



18760 



13 



yr. 







mo. to 



13 



yr. 



5 



mo. 



14500 



7 yr. 







mo. 



to 7 yr. 



5 



mo. 



18977 



13 



yr. 



6 



mo. to 



1?, 



yr. 



11 



mo. 





7 yr. 



6 



mo. 



to 7 yr. 



11 



mo. 



18939 



15 



yr. 







mo. to 



15 



yr. 



5 



mo. 



15000 



These observational means are shown as small circles in 

 figure 31. The ordinates are the pounds of milk produced and 

 the ages are the abscissas. From these observational means the 

 logarithmic curve, shown as the smooth curve of figure 31, is 

 calculated. The equation to this curve is 



y = 11,351.5 + 873.67 x — 32.225 x 2 + 1548.36 Log x 



