192 



TECHNICAL BULLETIN & 



portance. A knowledge of the part plaj'ed by environment as well as the part 

 played by inheritance in limiting the manifestation of a desirable character- 

 istic is well worth considering when breeding for egg production. Analytical 

 studies on the complex nature of fecundity should further disclose valuable 

 information that might otherwise be obscured. 



Character of Birds Used 



The birds used in this study are identical with those used in the two previ- 

 ous reports. Included are the records of all Rhode Island Red females 

 hatched from 1916 to 1924 in the experimental flock upon which pullet-year 

 trapnest records are available. The flock each year is made up of all the 

 daughters of each hen whose progeny was retained. The major portion of 

 the birds belong to tlie fecundity experiment. There are, however, a limited 

 number of birds bred for non-broodiness, some for intense broodiness, some 

 for hatchability, some for color, and a few inbreds that are included. Pullet- 

 year records are used exclusively in this study. 



The Coefficient oi Correlation 



The simple coeflicient of correlation is subject to certain limitations in bio- 

 logical data yet it affords a basis upon whicli to select groups of breeders and 

 also a basis for predicting future possibilities. Tlie fact is self-evident that 

 the simple coefficient of correlation is not an absolute measure of the degree 

 of association between the variables being studied because each variable may 

 be partially dependent upon other variables. For example, section 3 shows a 

 negative correlation of .6146 ± .0090 between age at first egg and annual 

 persistency. It is a known fact that both the dependent variable, age at first 

 egg, and the independent variable, annual persistency, are dependent upon 

 hatching date and environmental conditions, and that persistency is also de- 

 pendent upon weight at first egg and possibly upon length of winter pause. 

 The true relation between age at first egg and annual persistency could only 

 be arrived at by making the hatching date and environmental conditions con- 

 stant, as well as by making weight at first egg and winter pause duration 

 constant. Such procedure necessitates the use of partial coefficients of cor- 

 relation which require the use of the simple coefficient in their calculation. 

 Both the partial coefficient and the multiple coefficient will be employed in a 

 concluding bulletin of the series. Simple correlations are of very significant 

 practical value to tlie poultryman, however, in that tliey show him the relative 

 importance of different environmental influences and inherited character- 

 istics in relation to fecundity, and enable him to formulate his breeding pro- 

 gram accordingly. 



(A) Relation Between Environmental Conditions and Persistency 

 The only controllable environmental condition that will be considered in 

 relation to persistency is hatching date. Extreme care has been exercised 

 throughout the experiment to employ the same methods of feeding and brood- 

 ing. Hatching dates have been kept constant each year, but there have been 

 eight hatches each year at weekly intervals between March 2.5 and May 15. 

 The range in hatching date thus amounts to 49 days. Hatching date, how- 

 ever, may be controlled at will by the poultryman. 



