434 
Journal of Agricultural Research 
Vol. V, No. io 
It is evident from mere inspection of Tables I to VI that the correla¬ 
tion between these two variables is very high and that the regression is 
linear. Calculating the coefficients of correlation by the usual Bravais 
S(xv) 
formula, r= A - 7 --—? with a probable error of r given by the expression 
iV<r 1 <72 
I — 
PE r = ±.67449 —/=-> we have the results set forth in Table VII. 
-yn 
Table VII. —Coefficients of correlation between (a) egg production to March I and ( b ) 
egg production to 300 days of age 
Year. 
Flock. 
Coefficient of corre¬ 
lation. 
Barred Plymouth Rock. 
0. 955 ±0. 004 
• 939 ± -004 
• 9 2 3 ± • °°7 
.9i5± .005 
• 949 ± .005 
. 921± . 005 
IQII.... 
Total. 
IQII.... 
1912.... 
Barred Plymouth Rock. 
Total. 
1912 .... 
1913 .... 
IOI2 . 
Barred Plymouth Rock. 
Total. 
i y A o•••• 
These coefficients are clearly of a high order of magnitude. They fall 
in the same class, for example, as coefficients measuring the correlation 
between homologous organs on the two sides of bilaterally symmetrical 
organisms. These values in the present case lead unequivocally to the 
conclusion that with the flocks of birds here considered there certainly 
is no definite or marked superiority of either of these measures of the 
winter cycle of productivity over the other. These high correlations indi¬ 
cate that the two measures can be employed interchangeably so far as 
practical statistical work is concerned. This does not mean that the rec¬ 
ords to March 1 and to 300 days will be identical for a particular hen. 
What the high correlations do mean is that if an individual, A, has a 
higher record to March 1 than another individual, B, the probability is 
so high as to amount nearly to certainty that A will also have a record to 
300 days which will be higher than the corresponding record of indi¬ 
vidual B and by an amount in proportion to the difference exhibited by 
the records to March 1. 
It will be noted that the correlation for the total flock is lower than 
that for the Barred Plymouth Rock flock in every case. No biological 
significance appears to attach to these differences, which are small in 
amount. 
The three years here dealt with are entirely typical, and an exami¬ 
nation of our data indicates clearly that precisely the same result would 
be reached if we used the material from other years of the trap-nest rec¬ 
ords of the Maine Station. There was felt to be no point in piling up 
further correlation coefficients, all showing the same thing. The figures 
given above are quite sufficient to show that there is no warrant what- 
