8 MASS. EXPERIMENT STATION BULLETIN 416 



of the different measures of intensity. Since winter clutch size is generally used 

 here to measure intensity, it is important to know the intimacy of the correlation 

 between winter clutch size and annual egg production. The following constants 

 were determined: 



Number of birds 1470 



Mean winter clutch size — eggs 3.23 



Clutch size standard deviation ± L42 



Mean annual production — eggs 213.57 



Annual production standard deviation + 43.38 



Coefficient of correlation + .5011 + .0132 



Correlation ratio .5603 



Regression of annual production on winter clutch size was non-linear. The 

 correlation ratio, therefore, expresses the association. The value .5603 squared 

 indicates that about 31 percent of the variation in annual egg production is due 

 to variation in winter clutch size. The fact stands out clearly that winter clutch 

 size is a most important character affecting annual egg production. The value of 

 the association is considerably higher than that given in an earlier report (Hays 

 and Sanborn, 1927a), where r was .3544 ± .0117. 



Inheritance of High Intensity 



12. Correlation between Mothers and Daughters in Winter Clutch Size 



Winter clutch size is one measure of intensity that is inherited, according to 

 Hays and Sanborn (1927a). Other measures of intensity have alread}' been re- 

 ferred to, and the general belief is that rate or intensity of laying is governed by 

 inherited factors. One comm.on test that may be used is the coefficient of cor- 

 relation. There were available for study 258 mothers that produced 1470 daugh- 

 ters from which the following constants were derived: 



Number of dams 258 



Number of daughters 1470 



Mean winter clutch size of dams — eggs 3.74 



Clutch size standard deviation + 1.64 



Mean winter clutch size of daughters — eggs. . . . 3.23 



Clutch size standard deviation + 1.42 



Coefficient of correlation + .1365 + .0173 



The dams were, on the average, superior to their daughters in winter clutch 

 size. Dams and daughters were about equally variable in clutch size. Regres- 

 sion proved to be linear, and the correlation coefficient was .1365 ± .0173, which 

 was barely significant. This fact suggests that the dams were not breeding true 

 for high intensity and that more attention needs to be given to factors concerned 

 in the inheritance of high winter intensity. 



Relation of Intensity and Broodiness 



13. Winter Clutch Size in Relation to Broodiness 



Hays and Sanborn (1927a) pointed out that Rhode Island Red pullets that 

 exhibited the broo i\- instinct showed a larger mean winter clutch size than those 



