168 



TECHNICAL BULLETIN 8 



The Coefficient of Correlation. 



A general survey of a series of individual egg records myy lead to certain 

 general deductions some of which may actually be true and others false. The 

 breeder needs to know just how nnich stress to lay upon difl'erent character- 

 istics associated with the traits concerned in high fecundity. Tiie simple 

 correlation coefficient affords a concise measure of the degree of association 

 between specific traits and higii fecundity as well as a measure of the rela- 

 tionship between the presence of particular traits and high fecundity. The 

 correlation coefficient may thus l)e made use of by the breeder in two ways: 

 first, for prediction purposes; and second, in the selection of breeding stock 

 to obtain the most valuable combination of traits. Stated concisely, the cor- 

 relation coefficient is the only direct and specific measure for degree of 

 association of characteristics where large numbers of individuals are con- 

 cerned. Fecundity records may be modified by a vast number of environ- 

 mental conditions as well as by tiie live traits pointed out by Goodale and 

 Sanborn (1922) which are shown to be inherited. Hays (1924.). Only by 

 the use of large numbers of records made over a period of years under uni- 

 form conditions of management and in a ilock bred for uniformity can a 

 true value of the relative importance of characteristics concerned with fecun- 

 dity be approached. The coelT'cient of correlation thus becomes an invalu- 

 able tool in breeding for fecundity. 



Presentation of Data by Families. 



A study undertaken to consider the winter cycle and winter pause by 

 separate families would necessitate the presentation of page after page of 

 abstract data. Such data should be accompanied by detailed and complete 

 discussions and such general deductions as would seem justified. No definite 

 constants could be determined on numbers so small as the individual family. 

 Possibly all the descendants of particular individuals could be considered 

 as units, but from the genetic standpoint such a consideration should be 

 classed as questionable. A general tabulation of the whole population, 

 giving such information as mean hatching date, mean age at first egg, mean 

 weight at first egg, percentage of birds pausing, mean length of pause, mean 

 winter production, mean annual production, etc., by years could be made. 

 Such a tabulation would again be open to the criticism of not furnisliing 

 specific information. Only general deductions could be made and no evi- 

 dence would be furnished as to relative values. In view of the above facts, 

 this method of handling the data is not considered feasible. 



Winter Cycle 



Winter cycle may be considered in three general categories: namely, (a) 

 in its relation to environmental conditions, (b) in its relation to heritable 

 characteristics concerned in fecundity, and (c) in its absolute relation to egg 

 production. 



(a) Relation of Enviroiimental Conditions to Winter Cycle. 

 Hatching date belongs to the definitely controllable class of conditions in 

 tiiat it may be varied at will of the investigator. Date of first egg depends 



