BROODINESS AND FECUNDITY IN FOWL 



65 



Xiimher of birds . . . . 

 Mean times broody 

 Times broody standard deviation 

 Mean winter rate . . . . 

 Winter rate standard deviation 

 C<iefficient of correlation 



2221 



l.t3 



±1.99 



66.45 



±9.37 



4-.0706 



.0142 



Tiie above constants show the mean winter rate to be greater than the mean 

 December rate previously calculated. The above winter rate really signifies 

 that, on the average, the birds laid 66.45 per cent of the maximum possible 

 number of eggs when they were laying, since all pauses of four or more days 

 have been deducted in calculating winter rate. The standard deviation in 

 winter rate is only ± 9.37 compared with a figure of ± 20.40 for December 

 rate. The winter pause and the fact that many of the birds actually lay their 

 first egg during December account for the wider variability in December rate. 



The coefficient of correlation between times broody and winter rate is almost 

 identical with that Itetween times broody and December rate. This is a con- 

 stant of small magnitude, and is a false correlation because the population is 

 made up of both l)roody and non-broody birds. 



7. Correhttion Between Times Broody and Winter Rate for Broody Birds 

 .Hone — Pnllef Year. 



In order to ascertain any possible relationship between winter rate and 

 degree of broodiness, the correlation between times broody and winter rate 

 lias been calculated for broody birds alone. The constants obtained are as 

 follows: — 



Nuiuiier of liirds 



Mean times broody 



Times liroody standard deviation 



Mean winter rate 



Winter rate standard deviation 



Coefficient of correlation 



Regression broodiness on rate 



Regression rate on broodiness . 



1098 



2.89 



±1.93 



67.57 



±9.63 



—.0314 



—.0063 



—.1564 



.0203 



The mean winter rate in those birds that actually went broody during their 

 pullet year is 67.57 compared with 66.45 for broodies and non-broodies com- 

 bined. Such a difference is of no significance. 



The coefficient of correlation is negative. Its .small magnitude, together 

 with tlie size of its probable error, leads to the assumption that there is abso- 

 lute indeyiendence between winter rate and degree of broodiness as measured 

 iiy times broody. 



S. ('orreUifion Betrceen the Presence of Broodiness and Winter Rate above 

 the ^lean of Broodies and Non-Broodies Combined — Pullet Year. 



The absolute correlation between the presence of broodiness and high rate 

 is of importance to the breeder. Such a constant will indicate whether or not 

 the broodv trait carries with it higher winter intensity than does the non- 

 broody trait. The coefficient of correlation is calculated lielow according to 

 Yule. 



