TIME TO STANDARD EGG WEIGHT 3 



became sufficiently close to normal, giving a P value of .5143. It seemed de- 

 sirable, therefore, to use for the correlation studies only the 383 birds that gave 

 a normal distribution with respect to the dependent variable. Three independent 

 variables showed essentially normal distribution; four — hatching date, winter 

 pause, winter clutch, and persistency — did not. The partial or net coefficient of 

 correlation differs from the simple correlation coefficient in that in the calculation 

 of the former all other variables are held constant. For example, in calculating 

 the net correlation between hatching date (2) and time to standard egg weight 

 (1); age at first egg (3), weight at first egg (4), clutch size (5), pause duration (6), 

 days broody (7), and persistency (8) are all made constant. In calculating simple 

 correlations no allowance is made for variability in any of these characters. 



Correlation Between Hatching Date and Time to Standard Egg Weight 



In each of the five years covered by these studies, the birds were hatched in 

 eight weekly hatches beginning about March 25 and ending about May 15. 

 Yearly egg weight records are available only upon birds from the first three 

 hatches. The simple correlation between hatching date and days from first 

 egg to standard egg weight gave the following constants: 



Number of birds 383 



Mean hatching date (March 31) 1.8 



Hatching date standard deviation +.74 



Mean time to standard egg weight, days 106.93 



Time to standard egg weight standard deviation +48.33 



Coefficient of correlation — .1111+ .0340 



The standard deviation in time to standard egg weight shows that the popula- 

 tion was highly variable and suggests that this character must be influenced by a 

 large number of factors that may be both hereditary and environmental. 



The coefficient of correlation is negative and of sufficient magnitude to be 

 barely significant according to the criterion of Wallace and Snedecor (1931). 

 Its squared value, however, indicates that only about 1 per cent of the variation 

 in time required is due to differences in hatching dates. The regression was found 

 to be strictly linear, but the magnitude of the correlation coefficient in these 

 limited data does not signify an intimate relationship. 



The partial correlation coefficient between hatching date and time to standard egg 

 weight was calculated, keeping age at first egg, weight at first egg, clutch size, 

 pause days, broody days, and persistency constant. The value obtained was 

 ri2.345678 = — -5323, which indicates that hatching date does have an important 

 influence upon the time required to reach standard egg weight, and that early 

 hatching tends to increase the time necessary to attain standard egg weight. 



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



Early sexual maturity is known to be dominant to late sexual maturity. The 

 dividing line between genetically early and genetically late pullets falls at about 

 215 in the experiment station flock. Unpublished data indicate no genetic 

 difference with respect to age at sexual maturity between birds that begin to lay 

 when less than 216 days of age even though the range may extend from 140 to 



