THEORY OF STATISTICS.
For those exhibiting nerve signs :—
Proportion of the dull=(BD/(B)  . = 2 =a per cent,
og ,, defectively developed who
Sel a == 1573 ”
For those not exhibiting nerve signs :—
Proportion of the dull=(8D)/(8) i =e EES ys
Py ,,  defectively developed :
lla it = Eat
The results are extremely striking ; the association between A
and D is very high indeed both for the material as a whole (the
universe at large) and for those not exhibiting nerve-signs (the
B-universe), but it is very small for those who do exhibit nervesigns
 (the B-universe).
This result does not appear to be in accord with the conclusion
of the Report, as we have interpreted it, for the association
between A and D in the B-universe should in that case have
been very low instead of very high.
Example ii.—Eye-colour of grandparent, parent and child.
(Material from Sir Francis Galton’s Natural Inheritance (1889),
table 20, p. 216. The table only gives particulars for 78 large
families with not less than 6 brothers or sisters, so that the
material is hardly entirely representative, but serves as a good
illustration of the method.) The original data are treated as in
Example vii. of the last chapter (p. 33). Denoting a light-eyed
child by 4, parent by B, grandparent by C, every possible line of
descent is taken into account. Thus, taking the following two
lines of the table,
Children Parents Grandparents
A. a. B. B. C, vy
Light-eyed. Ted, Light-eyed. rd, Light-eyed. od
4 5 1 1 1 3
3 4 1 1 4 0
the first would give 4 x 1 x 1 =4 to the class ABC, 4x 1 x 3=12to
the class ABy, ¢ to ASC, 12 to 4By, 5 to «BC, 15 to aBy, 5 to
aC, and 15 to afy; the second would give 3x1x4=12 to the
class ABC, 12 to ABC, 16 to a BC, 16 to aC, and none to the remainder.
 The class-frequencies so derived from the whole table are,
(4B0C) 1928 (aBC) 303
(4 By) 596 (a By) 225
(480) 552 (aC) 395
(4B8y) 508 (ay) 501

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