to info page
in London 1863. Charles Spearman was educated in Leamington
College before joining the army. He moved through the
ranks and became a much decorated officer serving in Burma
and India. While in the military he became interested
in philosophy, it was this interest that prompted his
retirement from the army and promoted his study of psychology.
the age of 38 Spearman moved to Germany and studied experimental
psychology at the University of Leipzig. He earned his
Ph.D. in 1906 and then moved on to the University of Würzburg
and at then to the University of Göttingen.
of intelligence "g" and "s"
a strong statistical background, Spearman set out to estimate
the intelligence of twenty-four children in the village
school. In the course of his study, he realized that any
empirically observed correlation between two variables
will underestimate the "true" degree of relationship,
to the extent that there is inaccuracy or unreliability
in the measurement of those two variables. Further, if
the amount of unreliability is precisely known, it is
possible to "correct" the attenuated observed
correlation according to the formula (where r stands for
the correlation coefficient): r (true) = r (observed)
\ /reliability of variable 1 X reliability of variable
2. Using his correction formula, Spearman found "perfect"
relationships and inferred that "General Intelligence"
or "g" was in fact something real, and not merely
an arbitrary mathematical abstraction. He then discovered
yet another marvelous coincidence, the correlations were
positive and hierarchal. These discoveries lead Spearman
to the eventual development of a two-factor theory of
to the two-factor theory of intelligence, the performance
of any intellectual act requires some combination of "g",
which is available to the same individual to the same
degree for all intellectual acts, and of "specific
factors" or "s" which are specific to that
act and which varies in strength from one act to another.
If one knows how a person performs on one task that is
highly saturated with "g", one can safely predict
a similar level of performance for a another highly "g"
saturated task. Prediction of performance on tasks with
high "s" factors are less accurate. Nevertheless,
since "g" pervades all tasks, prediction will
be significantly better than chance. Thus, the most important
information to have about a person's intellectual ability
is an estimate of their "g"