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378
Hereditary Genius
APPENDIX.
THE deviations from an average are given in the following table of
M. Quetelet as far as 80 grades; they are intended to be reckoned on
either side of the average, and therefore extend over a total range of
160 grades. The eightieth is a deviation so extreme, that the chances
of its being exceeded (upwards or downwards, whichever of the two
events we please to select) is only (5000000-4999992)/10000000 =
8/10000000, or less than one in a million. That is to say, when firing at
a target (see Diagram, p. 28) less than one out of a million shots,
taking the average of many millions, will hit it at a greater height than
80 of Quetelet's grades above the mean of all the shots; and an
equally small number will hit it lower than the 80th grade below the
same mean.
Column M gives the chance of a shot falling into any given grade
(80 x 2 or) 160 in total number. Column N represents the chances
from another point of view; it is derived directly from M, and shows
the probability of a shot lying between any specified grade and the
mean; each figure in N consisting of the sum of all the figures in M
up to the grade in question, and inclusive. Thus, as we see by Column
M, the chance against a shot falling into the 1st grade (superior or
inferior, whichever we please to select) is .025225 to 1, and .025124
to 1 against its falling into
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