44 



BULLETIX 1090, r. S. DEPAETilEXT OF AGPJCULTURE. 



difference is greatest among the weights, but is great enough in th 

 other cases to make it reasonably certain that there are significan 

 differences among the fa mil ies, differences which might be expecte( 

 to persist, even though so many young were raised in each familT 

 that the standard deviation of each family mean became practically 

 zero. 



Table 2. — The differentiation among the inhred families. 



[The mean and standard deviation of the 22 family means relative to each of the characteristics studie< 

 is given for the ivro periods 1906 to 1910 and 1911 to 1915 (colimins 2, 3, 5, and 6;. The standard deviatioi 

 of family means exjjected from random sampling (columns 4 and 7) may be compared with the actua 

 standard deA-iations fcolumns 3 and 6;. The yearly rate of decline in each element of vigoris estimated 

 taking either the family (column 8; or the individual ("column 9; as the unit.] 



'< 't 



Character. 



1911-1915. 



Yearly decline. 



Mean 



of 

 family 

 means. 



a of means. 



Actual. 



Due to 

 chance. 



Mean 



of 

 family 

 means. 



0- of means. 



Actual. 



Due to 

 chance. 



iami- 



ly 



the 

 unit. 



Indi- 

 vidual 

 the 

 unit. 



Size of litter 



Litters per year 



Young per year 



Percentage born aUve 



Percentage raised of those born alive 

 Percentage raised 



Birth weight of all young 



Birth weight of young raised 



Gain to 33 days 



Weight at 33 days 



2.820 

 4.090 

 11. 536 

 Per 

 cent. 

 88.55 

 89.36 

 79.14 

 Grams. 

 83.95 

 86.86 

 165.18 

 252.04 



0.235 

 .321 

 1.302 

 Per 

 cent. 

 3.92 

 3.80 

 4.96 



Grams. 

 3.88 

 3.57 

 9.26 



12.17 



0.116 



Per 

 cent. 

 2.50 

 2.42 

 3.20 

 Grams. 



0.87 

 2.67 

 3.10 



2.492 

 3.303 

 8.227 

 Per 

 cent. 

 8.5.00 

 82.95 

 70.64 

 Grams. 

 81.82 

 85.00 

 146. 55 

 231. 55 



0.268 

 .383 

 1.226 

 Per 

 cent. 

 3.99 

 4.24 

 5.38 

 Grams. 

 4.19 

 4.57 



n.75 



15.02 



Per 



cent. 

 2.03 

 1.96 

 2.59 

 Grams. 



0.70 

 2.16 

 2.51 



0.08.5 



.203 



.853 



Per 



cent. 



0.92 



1.65 



2.19 



Grams. 



0.55 



.48 



4.80 



5.28 



0.04; 



.IK 



.45( 



Per 



cent. 



0.29 



1.04 



1,16 



Grams 



0.19 



1.19 



1,96 



2.15 



It will be noticed that, with one exception, the actual variation 

 among family means is greater in the second period than in the first, 

 in spite of the fact that the larger numbers born in the second period 

 have reduced the variation due to random sampling. In the case of 

 the one apparent exception, the num.ber of young produced per year, 

 the standard deviation is slightly smaller in the second period, but 

 the coefficient of variation is much greater, owing to the smaller mean. 

 It can thus be said with safety that there has been a pronounced 

 increase in the differentiation among the families in every respect 

 between the first and second periods. This increase in differentiation 

 is a natural consequence of the increasing homogeneity in each family. [ 



The unweighted average of the family means was calculated for 

 each character in each period, and a consideration of the results ; 

 brings out some interesting points. In every case the second period j 

 shows a marked decline compared with the first. This is in harmony 

 with the results described in Part I. It is to be noted, however, 

 that in the present figures the family is the unit, so that changes in 

 relative importance among the families have no effect on the results. 

 In order to make a comparison "v^dth the results obtained when aU ^ 

 families were combined we must calculate the average difference 



