~~ 
A.—_MATHEMATICAL AND PHYSICAL SCIENCES 31 
very simplest of cases that you can see relationships by merely plotting 
curves and comparing them. Statistical methods are inevitably forced 
on us by common sense when we want accurate and reliable inferences 
from series of data, just as a sextant is forced on a sailor when he wants 
to determine accurately the altitude of the sun. One who has lost an 
important lawsuit, owing to the ingenious argument of the opposing 
counsel, may object that by logic you can prove anything ; but that is 
an inadequate defence for being illogical on all occasions. As a matter 
of fact, when studying relations of cause and effect statistical methods 
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Fic. 4.—Illiteracy and unemployment. 
show us what quantities vary together, but strictly by themselves they 
tell us nothing as to causation. If we compare heights of fathers and 
sons, we learn that tall sons have tall fathers ; but in spite of that fact 
We are not convinced that the child is literally father to the man. 
Let us consider an example from data published in 1906 regarding 
‘unemployment and illiteracy as measured by the percentage of persons 
who could not sign their name in the marriage register (Fig. 4). Clearly 
the correlation coefficient between these two factors might lead to most 
undesirable inferences regarding the usefulness of education. But we 
could not expect to arrive at the truth if we ignored such an important 
fact as the amount of trade, and on admitting the data of this factor we 
See at once that faith in the value of our elementary schools need not be 
‘uprooted ; for the revival of prosperity produced marriage, especially 
among those in a humble position who could not write, as well as a 
