ANNUAL PERSISTENCY AND EGG PRODUCTION 193 



1. Correlation Between Hatching Date and Annual Persistency. 



The class interval for hatching date is seven days, and the class interval for 

 annual persistency is 15 days with a range of from 67 to 366 days. The fol- 

 lowing constants were calculated on 2179 birds: 



Number of birds .... 

 Mean hatching date (April IS) 

 Hatching date standard deviation . 

 Mean annual persistency . 

 Persistency standard deviation 

 Coefficient of correlation . 

 Regression hatching date on persistencv 

 Regression persistency on hatching date 



2179 



4.28 

 ±2.24 

 300.47 

 ±62.64 

 —.2208 ±.01 37 

 —.008 

 -6.187 



The above constants indicate that, on the average, the birds laid for 300 

 days before the onset of complete molt. This figure is somewhat lower than 

 it would be if maximum persistency had not been placed at 366 days, because 

 some of the birds laid for a greater time interval. The standard deviation 

 in persistency amounts to almost 63 days and furnishes statistical evidence 

 of very marked variability in persistency. 



The coefficient of correlation between hatching date and annual persistency 

 is negative and statistically significant. While this is not an intimate correla- 

 tion, it does demonstrate a tendency for early-hatched birds to lay longer 

 than late-hatched birds. The fact should be kept in mind, however, that the 

 earliest hatch was taken off each year about March 25 and that this date 

 should not be considered very early in this latitude. 



2. Correlation Between Hatching Date Eirlier than the Mean and High 

 Persist encg. 

 As previously stated, the birds have been di\ ided into two classes with 

 regard to persisteacv, namely, high and low. All birds are classed as high in 

 persistency when thev lay for 315 days or more before molting. Birds laying 

 for a shorter period than 315 days are classed as low. By dividing the popu- 

 lation of 2179 birds into these two classes for persistency, and by again classi- 

 fying these as hatched earlier or later than the population mean, an absolute 

 measure of the correlation between early hatching and high persistency is 

 obtained. The results of this classification follow: 



Hatching Date I High Persistency | Low Persistency 



Earlier than population mean 



720 ! 458 



Later than population mean 



416 I 585 



Totals 



1136 I 1043 



Coefficient of correlation -f. 3771 ±.0124 



