96 



Maine Agricultural Experiment Station. 1919. 



TABLE 2. 



Physical Constants for the Expected Milk and Butter-Fat Per- 

 centage of Jersey Registry of Merit cozvs, mothers and 

 daughters. 



Character 



Mean 



Standard 

 Deviation 



Coefficient 



of 

 Variation 



Quartile Limits 





First 



Median 



Third 



Daughter's Milk 



Production 

 Dam's Milk 



Production _ 



Daughter's 



Butter-Fat Per 



9547.6+44.7 

 9391.9±51.5 



5.558±.011 

 5.625±.013 



2114.4±31.6 

 2107.3±36.4 



0.5508±.0080 

 0.5546±.0093 



22.15±.35 

 22.44±.41 



9.91+.15 

 9.86±.17 



7982+61 

 7931±70 



5.174±.015 

 5.235+.018 



9213±56 

 8942±65 



5.559±.014 

 5.593±.016 



10780±.61 

 10403±70 



5. 938+. 015 



Dam's Butter-Pat 

 Per cent. - - . 



5.995±.018 



From table 2 it is possible to determine if on the average 

 the daughters of Jersey Registry of Merit cows are better than 

 their dams. The difference between the mean milk production 

 of the daughters from that of their dams is i"55.7±68.2, a dif- 

 ference which is certainly not significant. The difference be- 

 tween the mean butter-fat percentage of the daughters and their 

 dams is — o.o67±.oi7 or the difference is 3.9 times the prob- 

 able error. These facts lead to the conclusions that the mean 

 milk production of the daughters of Registry of Merit cows 

 does not differ from that of their dams and that to a small de- 

 gree these same daughters are slightly lower in butter-fat per- 

 centage than are the dams from which they came. 



The standard deviations for these tables give the necessary 

 information to determine the probable error of the mean gains 

 or losses of any number of pairs of daughters and their dams. 

 It has seemed best to base these calculations on the standard 

 deviations of the general population rather than on the stan- 

 dard deviations of the individual sires as it is believed the prob- 

 able error obtained will be more nearly its true value. The 

 calculation of this probable error of the mean gains or losses 

 is done by the usual probable error of the difference formula, 

 when the standard deviation of the difference is equal to 



2 r 1 2 



°"2 



(4) 



