44 



BULLETIN 1090, U. S. DEPARTMENT OF AGRICULTURE. 



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

 other cases to make it reasonably certain that there are significant 

 differences among the families, differences which might be expected 

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

 that the standard deviation of each family mean became practically 

 zero. 



Table 2. — The differentiation among the inbred families. 



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

 is given for the two periods 1906 to 1910 and 1911 to 1915 (columns 2, 3, 5, and 6). The standard deviation 

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

 standard deviations (columns 3 and 6). The yearly rate of decline in each element of vigor is estimated, 

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



Character. 



Size of litter 2. 820 



Litters per year 4. 090 



Young per year 11.536 



Per 



cent. 

 88.55 

 89.36 

 79.14 

 Grams. 



Birth weight of all young 83. 95 



Birth weight of young raised 



Gain t o 33 davs !l65. 18 



Weight at 33 days 1252. 04 



Percentage born alive 



Percentage raised of those born alive. 

 Percentage raised 



1906-1910. 



1911-1915. 



Mean 

 of 



family 

 means. 



<j of means. 



Actual. 



Due to 

 chance. 



0.235 

 .321 

 1.302 

 Ptr 

 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 



Mean 

 of 



family 

 means. 



2.492 

 3.303 

 8.227 

 Per 

 cent. 

 85.00 

 82.95 

 70.64 

 Grams. 

 81.82 

 85.00 

 146. 55 

 231.55 



a of means. 



Actual. 



0.268 

 .383 

 1.226 

 Per 

 cent. 

 3.99 

 4.24 

 5.38 

 Grams. 

 4.19 

 4.57 

 11.75 

 15.02 



Due to 

 chance. 



0.094 



Per 

 cent. 

 2.03 

 1.96 

 2.59 

 Grams. 



Yearly decline. 



Fami- 

 ly 

 the 



unit. 



0.70 

 2.16 

 2.51 



0.085 



.203 



.853 



Per 



cent. 



0.92 



1.65 



2.19 



Grams. 



0.55 



.48 



4.80 



5.28 



Indi- 

 vidual 

 the 

 unit. 



0.043 

 .110 

 .450 

 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 number 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 

 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 with the results obtained when all 

 families were combined we must calculate the average difference 



