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Born 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.

At 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.


Theory of intelligence "g" and "s"

With 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 intelligence.

According 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"


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