78 MASS. EXPERIMENT STATION BULLETIN 264 



5. Total Days Broody versus Length of Molt Period. 



Of the total of 924 birds used in this study, 242 or 26.19 per cent became 

 broody during their pullet year. The 682 individuals not manifesting broodi- 

 ness the first year had an average molt period of 78.45 days. 



Broodiness appeared in varying degrees in the broody population. In the 

 broody population used in the correlation studies there was a range of from 

 2 or 3 days up to 170 days spent in broodiness during the first laying year. 

 Class intervals of 10 days were used and the broody birds classified with 

 respect to total days broody and duration of molt period. The following ar€ 

 thet constants obtained: 



Number of birds- 242 



Mean length of molt period— days 67.-54 



Molt period standard deviation — days ±29.98 



Mean days broody _ _ 42.61 



Days l)roody standard deviation _ ±35.-53 



Coefficient of correlation —.0736 ± .0431 



Correlation ratio _ .2136 



The mean length of the molt period in the broody population was 67.54 

 days, while the mean length of molt period for the non^broody population was 

 78.45 days. This difference is of considerable importance from the standpoint 

 of egg production. Evidence has been discovered (Hays and Sanborn, 1927 a) 

 to indicate that genes for broodiness and genes for high intensity show a de- 

 gree of linkage, and Section 3 of this report suggests that intense layers 

 molt in a shorter period than ordinary layers^ The interrelationship of brood- 

 iness to intensity and of intensity to length of molt probably accounts for the 

 shorter period in broody birds. 



The broody population showed a mean of 42.61 days lost to production 

 while broody during the pullet laying year. The magnitude of the standard 

 deviation in broodiness indicatesi the extreme variability of the population, 

 which was due to varying numbers of broody periods and not to variable 

 length of broody periods. 



The coefficient of correlation between total days broody and length of molt 

 period was — .0736 ± .0431. This constant is of no significance and indicates 

 that the length of the molt period was independent of degree of broodiness. 



The correlation ratio of molt period to total days broody was .2136 which 

 is almost three times the value of the coefficient of correlation. (Correlation 

 ratio) = — r=r:=.0402± .0167. The difference is only 2.41 times its probabk 

 error by Blakeman's test, which suggests that the difference between the 

 correlation ratio and the correlation coefficient is not significant. 



A test for linearity of regression of duration of molt on total days broody 

 by the X- method gave a probability of linearity of .8766 which again suggests 

 that the relation between length of molt period and total days broody was 

 close enough to linearity to make the coefficient of correlation the best 

 measure of association. 



6. Anvnual Persistency versus Length of Molt Period. 



Since annual persistency has been shown by Hays and Sanborn (1927 b) to 

 be the most important single heritable characteristic affecting pullet year 



