INHERITANCE OF INTENSITY 9 



SECTION 3. INTRACLASS CORRELATIONS 



In order to secure further evidence on the inheritance phase of intensity as 

 measured by clutch size, intraclass correlations were calculated and are shown in 

 Table 3. The population of daughters was grouped by sires and by dams. Evi- 

 dence regarding sex linkage will also be brought to light. 



Table 3. — Intraclass Correlations. 



*Not significant according to the value of F. 



Mx — M 



The common formula ri = ^ -\-(k ^\'^/^ given by Snedecor (1946, p. 245) was 



made use of. Dams were grouped into low, medium, and high phenotypes as was 

 done in Table 1. Since all daughters were exposed to similar environmental con- 

 ditions, the intraclass correlations should represent the inheritance phase. 



The constants in Table 3 supply no evidence of sex-linked factors operating to 

 regulate clutch size. These constants, with but three exceptions, indicate that 

 heredity operates to regulate clutch size. Clutch size during September and 

 October at the close of the laying year does not exhibit an important hereditary 

 phase. In general, there was a higher intraclass correlation in daughters from 

 low intensity dams. 



Compared with the insignificant simple correlations between mothers and 

 daughters, the intraclass correlations stress the importance of selecting breeding 

 females on the basis of family means, which are logically a better measure of 

 breeding ability than are individual records. These data support the ideas set 

 forth by Lerner and Taylor (1943) that there are good opportunities for raising 

 the level of intensity by selective breeding in improved flocks. 



SECTION 4. RATE OF LAYING AS A MEASURE OF INTENSITY 



Gross and net rates of laying were calculated on mothers and daughters, all 

 calculations being made on the first laying year. Gross rates were calculated as 

 follows: winter rate, number of eggs laid from first egg to March 1, divided by 



