SUPPLEMENTS—GOODNESS OF FIT. 
Fev +, 
Flower, Total. 
Prickly. Smooth. 
: : 47 12 £) 
Violet 48-337 10-663 
hi 21 3 “A 
Shite 19-663 4337 
Total . : 
Here 6 is 1-337, and 
1 1 1 1 
2 (1-337 | am Gees roses 1337) 
X= (357) feamr + 10063 T9603 4337 
=-708. 
Turning up this value of x? in the table on p. 385, we find by 
interpolation P=-400. As stated in the text, the association, 
negative in this case, is “so small that no stress can be laid on it 
as indicating anytLing but a fluctuation of sampling.” 
Precisely the same result can be arrived at by working out the 
standard error of the difference between the proportions of violet 
and of white flowers that have smooth fruits, taking the ratio of 
the difference to its standard error and then using the table of 
areas of the normal curve. Thus:— 
Proportion of violet flowers that have smooth 
fruits, 12/59 or . "2033 
Proportion of white flowers that have smooth 
fruits, 3/24 or : . "1250 
Difference . 0783 
Proportion of all flowers that have smooth fruits, 
15/83 or "1807 
Standard error of the difference between proportions of smooth 
fruits in sampling from a universe in which the proportions are 
‘1807 and '8193, and the numbers in the samples 59 and 24 
respectively :— 
bt.) 
8193 x 1807 93) = 0932. 
V X 59 Tog 
Hence the ratio of the observed difference to its standard error is 
‘0783/:0932 or ‘840. 
381 
i auit 
at 
24 
68 15 83