166 Blood Fat in Fowls 



should be of a general and vague nature. Correlation is a verj 

 definite quantitative phenomenon, measurable on a universalh 

 applicable scale of 1 to + 1 . The numerical value of the cor 

 relation coefficient, r, may be determined in any instance for twi 

 measured variables, such for example, as fat content and annua 

 egg record, by very simple and well known formulas. 



We now turn to the actual results which may be obtained b 

 applying the correlation formulas 11 to the data published by Wui 

 ner and Edmond. Using a simple method of direct summatio 

 of the actual values, their squares and their products, 12 we find th 

 following results for the whole series of 1 year old hens : 13 



r fe = +0.247 0.076 



Thus, taking the whole series of 1 year old birds examined, tl 

 hens which have a larger amount of fat in their blood in Octobi 

 have, on the average, laid a larger number of eggs during the yea 



11 Warner and Edmond must have been fully acquainted with the a 

 vantages of applying the correlation formulas to such problems as the; 

 for the data contained in the preliminary papers by Blakeslee and Warm 

 cited and discussed by Warner and Edmond, together with far more extf 

 sive data collected since these two preliminary papers were published, ha 

 been carefully treated in great detail by the statistical methods in a paj 

 by Harris, Blakeslee, and Warner (Genetics, 1917, ii, 36; Proc. Nat. An 

 Sc., 1917, iii, 237). These papers, like that by Lawrence and Riddle, tl: 

 have, quite inadvertently, failed to cite, although they contain much tl 

 throws light upon the problems considered by them. A further investi: 

 tion of the problem of the interrelationship between egg laying activ 

 at various periods which also contains materials bearing very direc 

 upon the problem of the physiology of egg production is now in pr 

 (Genetics, 1918, iii, 27). 



12 Harris, J. A., Am. Naturalist, 1910, xliv, 693. 



13 Those unfamiliar with statistical formulas need only remember t ; 

 the correlation coefficient measures the intensity of interrelations! ; 

 between two variables on the scale of 1 to +1. Thus if annual egg f 

 duction is lower in birds with lower percentages of fat and higher in bi 3 

 with higher percentages of fat correlation between egg production and t 

 content is positive in sign and lies somewhere between no correlation 1 

 perfect correlation. If high annual egg record is associated with low t 

 content and low annual record with high fat content, correlation is nega a 

 in sign and is measured by a coefficient lying between and perfect n&amp;lt; 

 tive correlation. 



