88 Report of DepxVrtment of Animal Industry of the 



the 13 cows during these two years was 155,308 lbs., that for 

 1898 being the smaller by 8,712 lbs. or 5.6 per ct. Likewise in 

 Bulletin 102 of the Wisconsin Station^ there is given the annual 

 yield of 27 cows during two years. The total yield was 398,690 

 lbs. with a difference of 4,128 lbs. or 1 per ct. in favor of the 

 second year. Combining the data from these two groups in such 

 a way as to reduce the variation as far as possible the yield of 

 these 40 cows during two succeeding years varied by 4,584 lbs. 

 which was .82 per ct. of the total yield during a time equivalent 

 to 80 lactation periods. 



From this data it would appear plain that the increase of 1 per 

 ct. in yield during the hand milking of the cows as given in 

 Table III is clearly within the variation which may reasonably 

 be expected from the annual fluctuations in the yield of cows. 



The fact that the final balance in favor of the hand method 

 in Table III is merely an accidental result of the method of 

 grouping the data is well illustrated by arranging the data on a 

 slightly different but equally logical basis. If the comparison 

 of the othc'rwise satisfactory data be restricted to those cases 

 where there are data for an even number of successive years for 

 one cow milked alternately by the two methods, the data from 

 nine lactation periods will be rejected. The data thus selected 

 are given in Table IV. 



This arrangement of the data shows that in the 62 lactation 

 periods, 31 of which were with hand milking and 31 with ma- 

 chine milking, 3,285 pounds more milk were obtained by the 

 machine than by hand. Here again the difference is unimportant 

 being only 0.8 per ct. of the total milk obtained. Had the 

 yields of cow No. 10 for 1906 and 1907 been omitted the balance 

 would have been 909 pounds in favor of hand milking. Here 

 also the accumulated variation between two groups of 31 mem- 

 bers each is less than the variation between individual members 

 of the group. 



1 Carlyle, W. L., and Woll, F. W. Studies in milk production. Wis. Agr. 

 Exp. Station Bui. 102. 1903. 



