4 MASS. EXPERIMENT STATION BULLETIN 313 



215 days. It is assumed, therefore, that such variability in age is due to en- 

 vironmental forces. 



The simple correlation coefficient was calculated between age at first egg and 

 time to standard egg weight using only genetically early-maturing birds. The 

 constants obtained are as follows: 



Number of birds 383 



Mean age at first egg, days 178.76 



Age at first egg standard deviation ± 16.28 



Mean time to standard egg weight, days 106.93 



Time to standard egg weight standard deviation ±48.33 



Coefficient of correlation — .41 74 ± .0285 



The variability in age at first egg amounts to about 9 per cent in the popula- 

 tion. As already stated, it is probable that this variability is due entirely to 

 environmental causes. 



The coefficient of correlation is negative and indicates that age differences play 

 an important role in time to standard egg weight. The regression in this case 

 is strictly linear. 



The partial correlation between these two variables, when the other six variables 

 are held constant is ri3.24567S= — .6419, which clearly indicates that age at sexual 

 maturity greatly influences the time to standard egg weight. 



In the population studied, the mean average age at which standard egg weight 

 was attained was found to be 285.21 days. This fact indicates that the Rhode 

 Island Red pullets used in these studies tend to begin laying 24-ounce eggs at 

 not far from ten months of age. It seems probable, according to the work of 

 Waters (1931) with Leghorns and Brahmas, that this may also be the age when 

 complete body growth is attained. 



Correlation Between Weight at First Egg and Time to Standard Egg Weight 



Each pullet was weighed on the day that she laid her first egg. Since there 

 is a positive correlation between body weight and egg size, there may also be an 

 association between weight at first pullet egg and time to standard egg weight. 

 The correlation was calculated for the population being studied. 



Number of birds 383 



Mean weight at first egg, pounds 5.40 



Weight at first egg standard deviation +.56 



Mean time to standard egg weight, days 106.93 



Time to standard egg weight standard deviation ±48.33 



Coefficient of correlation —.2317 ±.0326 



Body weight shows a variability of about 10 per cent, probably due largely to 

 age differences, as Hays (1933) pointed out. The coefficient of correlation is 

 negative and indicates by its value squared that about 5 per cent of the variability 

 in time required is due to weight differences at first egg. The regression was 

 essentially linear. 



The partial correlation between weight at first egg and time to standard egg 

 weight was —.3307. This constant indicates further that body weight at sexual 

 maturity does not have a very great influence upon the time to standard egg 

 weight. 



