6 MASS EXPERIMENT STATION BULLETIN 313 



and time interval to standard egg weight. 



Correlation Between Total Days Broody and Time to Standard Egg Weight 



There were only 49 individuals showing broodiness during the pullet laying 

 year. The total days broody for each bird were determined by adding together 

 the non-productive days associated with broody periods. The simple correlation 

 between total days broody and time to standard egg weight was calculated, 

 giving the following constants: 



Number of birds 49 



Mean days broody 31.42 



Broody days standard deviation ±25.94 



Mean time to standard egg weight, days 119.75 



Time to standard egg weight standard deviation ±45.36 



Coefficient of correlation +.2679 ± .0894 



Standard deviation in days broody shows striking variability. This is in 

 agreement with the observation previously reported by Hays (1933) that degree 

 of broodiness is inherited. Mean time to standard egg weight was slightly greater 

 in the broody population than in the group that did not show broodiness the 

 first year. The means are 119.73 and 104.90 respectively. 



The correlation coefficient between days broody and time to standard egg 

 weight is positive but not significant as judged by its probable error or by Wallace 

 and Snedecor's criterion. The regression is strictly linear. From these limited 

 data, the time required to standard egg weight does not appear to be associated 

 with non-productive time due to broodiness. 



The partial correlation between days broody and time to standard egg weight 

 does, however, show a significant relationship. This constant was found to be 

 +.4210, which indicates that about 18 per cent of the variation in time required 

 is due to differences in degree of broodiness. 



Correlation Between Annual Persistency and Time to Standard Egg Weight 



Annual persistency records are available on 297 birds in the population studied. 

 The remaining 86 individuals failed to complete their 365-day egg record, generally 

 because of death or disease. Annual persistency was represented by the time 

 from first pullet egg to a 30-day pause after March 1 or to the close of the 365-day 

 laying year, if no 30-day pause occurred previously. Thus the maximum persis- 

 tency was 365 days even though the bird may have continued to la)-. Calculation 

 of the correlation between annual persistency and time to standard egg weight 

 gave the constants below: 



Number of birds 297 



Mean annual persistency, days 344.51 



Annual persistency standard deviation ±33.44 



Mean time to standard egg weight, days 107.34 



Time to standard egg weight standard deviation ±48.21 



Coefficient of correlation - .0100 ± .0391 



Annual persistency, like age at sexual maturity, showed a variability of about 

 9 per cent. The mean persistency of 344.51 days indicates that most of the 

 birds were genetically highly persistent. The mean time to standard egg weight 



