45 



in question is from 3.75 (6.68 - 2.95 = 3.7.5) to 9.63 (6.68 + 2.95). The 

 probable error is written with a ± sign after each coefficient of correlation. It 

 is used as a measure of the reliability of the figure given. Thus the degree of 

 correlation between hatching date and weight at 150 days is —.3293 ± .0194. 

 The meaning is that if we add .0194 to the coefficient of correlation and also 

 subtract .0194 from the coefficient of correlation, we obtain two figures, namely, 

 .3099 and .3487. The chances are even that the true coefficient of correlation 

 between hatching date and 150-day weight lies inside or outside of these limits. 

 A coefficient of correlation at least three times as large as its probable error is 

 considered as significant. 



Hatching Date 



Part of the data is presented below in tabular form to show the general re- 

 lation of hatching date to weight at 150 days, weight at first egg, age at first 

 egg, and winter production, together with the average number of birds con- 

 cerned in all four cases. This table will be particularly useful for general 

 reference. 



Table 1. 



The 150-day weight is observed to decrease rather regularly as the date of 

 hatching advances. This fact substantiates common observation that early 

 hatching seems to be associated with rapid growth. The weight at first egg 

 for the different hatches shows little consistency, but as a rule, the earlier 

 hatched birds appear to be somewhat heavier than the late hatched. The 

 inconsistency is no doubt due in large measure to the wide range in age at first 

 egg. Age at first egg seems to be but little dependent upon hatching date. 

 In the last three or four hatches, however, there appears to be a reduction in 

 the average age at first egg. Hatching date is intimately associated with 

 winter production. In other words, the early broods as a rule lay more winter 

 eggs than later broods. In general, hatching date appears to influence the 

 weight at 150 days and the winter production with probably some influence 

 upon weight at first egg and age at first egg. 



As already stated, the pullets were hatched at one week intervals beginning 

 March 25 and ending June 3. Thus eleven different age groups are repre- 

 sented with a range in age of 70 days. Hatching date is studied in relation to 

 weight at 150 days, weight at first egg, age at first egg, and winter production: 



Hatching Date versus Weight at 150 Dai/s 



Number of birds 959 



Mean hatching date 6.68 



Hatching date standard deviation .... ±2.95 



Mean 150-day weight 3.96 



150-dav weight standard deviation .... ±.56 



Coefficient of correlation -.3293±.0194 



The fact will be noted that the mean hatching date is 6.68 (May 4) instead 

 of 6.00 (April 29) as would be the case if each hatch had produced the same 



