A Cooperative Stiidi/ 
329 
The order of mottling categories seems to correspond as closely as we can 
determine from the plate to the order of relative amount of mottling. 
We find for the mean rj when there is no association : 
= -004521. 
Hence ij' corrected for number of arrays but not for class-index is given by 
-004,702 - 004,521 
^= ^83 =0001817, 
or ■ 7j' = -0135. 
This is insignificant and therefore we need not trouble to find the class-index 
correction. It would not appear therefore that the brown eggs are more densely 
mottled than the green eggs. 
We now pass to intensity of groimd colour. It will be remembered that two 
scales were formed of ' values ' giving as far as possible equal values by the same 
letters for both gi'een and brown colours. 
TABLE XVI. 
Coloui' and Value. 
Ground Colour Values. 
Colour of Egg 
A 
B 
C 
D 
E 
F+G 
H + I+K 
Totals 
Brown 
5-2 
76 
6.3 
95 
51 
44 
56 
437 
Green 
34 
51 
71 
133 
85 
154 
141 
669 
Totals ... 
86 
127 
1.34 
228 
136 
198 
197 
1106 
It is clear on the face of this table that the percentage of high values in the 
brown series is far greater than in the green series, which has a much greater 
percentage of low-colour values. To get an appreciation of this association we use 
biserial rj. We have for zero association 
T = •005,425, 
while uncorrected t?'^ = "113,734. 
Accordingly corrected for a number of arrays 
-113,734 --005,425 .... 
= ^5:479 = 108'8009, 
leading to t?" = -3299. 
Calculating the class-index correlation, we find it -9674 and thus finally 
corrected 
7/^-3410 + -0197. 
Biometrika xii '22 
