4 MASS. EXPERIMENT STATION BULLETIN No. 286 



correlation coefficient, the value .1740 appears. The interpretation is that aliout 

 17 per cent of the variability in spring clutch size may be accounted for as due 

 to variability in winter clutch size. Such an association is certainly genetically 

 significant though not very intimate. 



2. Correlation Between Whiter and Summer Clutch Size. 



Mean summer clutch size represents the constant obtained by dividing the 

 number of eggs laid from June first to the end of the 365-day laying year by the 

 number of clutches involved. Records are available on 1682 birds, and winter 

 clutch was paired against summer clutch for each bird with class intervals of 

 one. The calculations show the following constants: 



Number of birds 1682 



Mean winter clutch 3.35 



Winter clutch standard deviation ±1.60 



Mean summer clutch 3.04 



Summer clutch standard deviation ±1.60 



Coefficient of correlation +.2829±.0151 



Correlation ratio .3091 



Mean clutch size during the winter months is somewhat greater than during 

 summer. The variability in summer clutch size is also greater than for winter 

 clutch size. The lesser variability in size of clutch during winter shows that the 

 flock is more uniform in winter than in summer production. 



Regression of summer clutch size on winter clutch size is not strictly linear 

 by Blakeman's test. The correlation ratio is therefore used to measure the 

 association. The constant +.3091 expresses a less intimate association between 

 winter clutch size and summer clutch size than was observed between winter 

 clutch and spring clutch with a constant +.4171. The squared value of .3091 

 is .0955 showing that about 10 per cent of the variance in summer clutch size 

 may be associated with variance in winter clutch. Winter clutch size may be 

 said to have a value for selection purposes of about 10 per cent as affecting sum- 

 mer clutch size. 



3. Correlation Between Spring and Summer Clutch Size. 



The spring period of March, April and May is the normal laying period for 

 the imimproved domestic hen. Flocks bred for high fecundity differ greatly 

 from unimproved flocks in the distribution of egg laying during the pullet year. 

 For example, the Massachusetts Agricultural Experiment Station flock hatched 

 in 1913 laid about 29 per cent of the yearly average by the end of February. 

 The flock hatched in 1930 averaged to lay about 36 per cent of its eggs before 

 March first. Moreover, the actual mean length of the productive year has in- 

 creased from about 240 days to 340 days. These changes have reduced the pro- 

 portion of total eggs laid during the spring season and this section is chiefly 

 concerned with possible inter-relations of intensity, between the spring and 

 summer periods. 



The coefficient of correlation between mean spring clutch and mean summer 

 clutch was calculated on 1682 birds to discover if there is a significant associa- 

 tion. The constants are presented below: 





