80 MASS. EXPERIMENT STATION BULLETIN 264 



920 birds. These were tabulated in a correlation table giving the following 

 constants: 



Number of birds _. 920 



Mean length of molt period — days 75.27 



Molt period standard deviation — days ±29.99 



Mean weight at first egg — lbs 5.36 



Weight standard deviation— lbs _. ±.58 



Coefficient of correlation +.1457 ± ,0218 



Correla tion ratio _ „ .1741 



The magnitude of the standard deviation in weight indicates that the birds 

 varied rather widely in weight when they laid their first egg. The extreme 

 range in weight was from 3.50 pounds to 7.50 pounds. Class intervals of 

 one^half pound were used for classification. 



The positive coefficient of correlation of .1457 ± .0218 is of no statistical 

 significance according to tlie criteria adopted in these studies. 



The correlation ratio of duration of molt to weight at first egg was also 

 of small absolute magnitude. By Blakenian's criterion, the difference be- 

 tween the correlation ratio and correlation coefficient was only 2.17 times its 

 probable error and cannot be considered as significant. This fact indicates 

 that the relationship between duration of molt period and body weight was 

 linear. 



The regression of length of molt on body weight by the X^ test gave a 

 probability of linearity of .6678, when six birds weighing less than four 

 pounds at first egg were omitted. From these facts it seems reasonable to 

 assume that the correlation coefficient correctly measures the relationship de- 

 sired, but that the correlation between duration of molt and body weight at 

 first egg is insignificant. 



8. Gain in Weight During the Laying Year versus Length of Molt Period. 



Body weight records at the beginning and end of tlie pullet laying year are 

 available on 305 birds. It is possible, therefore, to calculate the gain or loss 

 of each individual. In the population of 305 there were 60 individuals show- 

 ing either no change or a loss in weight during the laying year. This group 

 of 60 birds had a mean molt period of 72.17 days and may be compared wit!h 

 the gaining group below. 



A total of 245 molting birds showed a gain in weight during the pullet 

 laying yiear. These birds were classified with respect to weight increase using 

 quarter-pound class intervals, and with respect to molt using 10-day class 

 intervals. The following constants were derived: 



Numiber of birds 245 



Mean length of molt period — days 65.23 



Molt period standard deviation — days :. 24.88 



Miean weight increase — lbs .67 



Weight increase standard deviation — lbs — ±.41 



Coefficient of correlation —.1220 ± .0424 



Correlation ratio .2315 



