Spearman, Charles

Charles Spearman (1863–1945) is the originator of the two-factor intelligence theory, the father of factor analysis, and a pioneer of the classical test theory. Spearman was born to a well-known family in London. After he graduated from Learmington College, he joined the British army and became a much-decorated officer in Burma and India. While in the army, he developed his interest first in philosophy and later in psychology. He earned his PhD with Wilhelm Wundt from the University of Leipzig, in Germany, in 1906. From 1907 to 1931, he worked at University College, London, first as a reader in experimental psychology and then as a professor of mind and logic. He conducted psychological research for the army during the First World War. After his retirement as an emeritus professor from University College, he traveled and taught in the United States, India, and Egypt. He received several honors in Britain, Germany, and the United States.

In 1904, Spearman published “The Proof and Measurement of Association Between Two Things,” in the American Journal of Psychology. In this article, Spearman proposed that the correlation between two variables could be weakened by errors of measurement. To restore the true relationship between variables p and q, Spearman invented the attenuation correction formula:

meaning that the true correlation coefficient between p and q equals the observed correlation coefficient [Page 944]divided by the square root of the product of the reliability coefficients of variables p and q. Using this formula, Spearman calculated the correlations between various measures of mental abilities obtained at the time and identified an overall mental ability or general intelligence. This concept of general intelligence, or “g,” became the focus of his second article, “General Intelligence Objectively Determined and Measured,” which was published in the same year. In this landmark article, Spearman proposed that the “g” factor underlies all human abilities. In addition to this “g,” there is a second level of specific factors, or “s,” that account for the differences among various specific abilities. Any act of human intellect is a function of both the “g” and “s” factors. In his development of the two-factor intelligence theory, Spearman became the pioneer of a new statistical procedure, namely factor analysis. His concepts about true score and measurement errors became the basis of the classical test theory. His interest in statistics also led him to develop the Spearman rho, a correlation coefficient to be used when a sample size is small and data are in rank order. He is also accredited with the SpearmanBrown prophecy formula, which predicts test reliability based on the size of a test. Spearman's influence in the fields of psychology and education can still be felt today, especially through his twofactor intelligence theory. Other works published by Spearman include “The Nature of Intelligence and the Principles of Cognition” (1923), “The Abilities of Man: Their Nature and Measurement” (1927), “Creative Mind” (1930), and “Psychology Down the Ages” (1937).