es 2 1 1 1

Stephen 1 4 3 9

Thomas 4 2 2 4

William 6 7 1 1

n = 7

sum of D[squared] = 24

n[squared] - 1 = 48

6 x sum of D[squared] = 144

6 x sum of D[squared] / n ( n[squared] - 1 )

= 1 - 144/(7 x 48)

= +.57

In order to get a full and true measure of the correlation between
two tests, the following precautions are necessary:

(1) The _same individuals_ must be given both tests.

(2) The number of individuals tested must be as great as 15 or 20,
preferably more.

(3) The individuals should be a fair sample of the population in
regard to the abilities tested; they should not be so selected as to
represent only a small part of the total range of ability.

(4) The tests should be thorough enough to determine each
individual's rank in each test, with a high degree of certainty.
Sloppy testing gives a correlation nearer zero than it should be,
because it "pies" the true orders to some extent.
[End footnote]

{285}

General Factors in Intelligence

If now we try to analyze intelligence and see in what it consists, we
can best proceed by reviewing the intelligence tests, and asking how
it is that an individual succeeds in them. Passing the tests is a very
specific instance of {286} intelligent behavior, and an analysis of
the content of the tests should throw some light on the nature of
intelligence.

The first thing that strikes the eye in looking over the tests is that
they call for so many different reactions. They call on you to name
objects, to copy a square, to tell whether a given statement is true
or false, to tell wherein two objects are alike or different. The
first impression, then, is that intelligence consists simply in doing
a miscellaneous lot of things and doing them right.

But can we not state in more general terms how the individual who
scores high in the tests differs from one who scores low? If you
survey the test questions carefully, you begin to see that the person
who passes them must possess certain general characteristics, and that
lack of these characteristics will lead to a low score. We may speak
of these characteristics as "general factors" in intelligent behavior.

First, the tests evidently require the use of past experience. They
call, not for inst