4 MASS. EXPERIMENT STATION BULLETIN 298 



The correlation between pause duration and length of the biological year is of 

 questionable value since its squared value (.0304) indicates that only about 3 

 per cent of the variation in duration of the biological year is associated with 

 variation in pause duration. .As a selection unit for increasing the length of the 

 biological year, pause tiuration is of very little value. 



3. Relation Between Winter Cluteh Size and Len^h of Biological Year. 



Mean winter clutch size has been used extensively at this Station as a measure 

 of intensity or rate of laying. Rate of laying is distinctly an inherited character 

 as Hays and Sanborn (1927b) have shown. Correlation studies have been made to 

 discover whether the rate of winter laying shows any relation to the length of the 

 biological year. The constants calculated are as follows: 



Number of birds 910 



Mean winter clutch — eggs 3.49 



Winter clutch standard deviation +1.77 



Mean biological year — days 363.92 



Biological year standard deviation +42.19 



Coefificient of correlation +.0590. +0223 



Correlation ratio .2251 +.02 12 



Blakeman's test indicates that the regression of biological year on clutch size 

 is non-linear. Hence the correlation ratio measures the association between the 

 two variables. The association is positive, indicating that to some extent the more 

 intense winter layers tend to lay for a longer period than the less intense layers. 

 The squared value of the correlation ratio is .0507, which suggests that only 5 

 per cent of the variation in duration of biological year is due to clutch size varia- 

 tion. 



4. Relation Between Days Broody and Length of the Biological Year. 



The total number of non-productive days spent in broody periods during the 

 pullet laying year is an indication of degree of broodiness. There is evidence in 

 this flock that degree of broodiness depends upon inheritance. If a broody period 

 serves as a recuperative period for the reproductive system, the anticipated result 

 might be a greater duration of the biological year in the more intense broody 

 individuals. In this study only individuals showing one or more broody periods 

 are included in the correlation table. The constants derived are as follows: 



Number of birds 191 



Mean total days broody 33.04 



Total days broody standard deviation J;^26.28 



Mean biological year — days 358.26 



Biological year standard deviation +50.57 



Coefficient of correlation -.0633 + .0486 



Correlation ratio .2907 +.0447 



The extreme variability in degree of broodiness is very striking. The mean is 



33.04 days with a standard deviation of 26.28, making the coefficient of variation 



79.5 per cent. 



The negative coefficient of correlation is statistically insignificant, but the re- 

 gression is non-linear. The correlation ratio indicates that the more intensely 

 broody birds are likely to exhibit a shorter biological year. The squared value 

 of the correlation ratio shows that about 8.45 per cent of the variation in length of 

 biological year is due to \ariation in degree of broodiness. 



