Charles Spearman

William Revelle Northwestern University

Charles Spearman (1863-1945) was the leading psychometrician of the early 20th century. His work on the classical test theory, , and the g theory of intelligence continues to influence psychometrics, , and the study of intelligence. More than 100 years after their publication, his most influential papers remain two of the most frequently cited articles in psychometrics and intelligence.

Charles Edward Spearman (born: , Septem- Spearman. ber 10, 1863; died London, September 17, 1945) was the leading psychometrician of the early 20th A late start century. He was the founder and head of the “Lon- don School” of psychology at University College, Spearman came late to psychology, having been London (UCL) where he and his many students an officer in the 2nd Battalion of the Royal Mun- combined an experimental with a psychometric ap- ster Fusiliers in India from 1885 to 1897. The proach to the study of cognitive ability. He be- last two years he spent (1895-1896) in the British came Reader in Experimental Psychology at UCL Staff College near London where his education in- in 1907 and was made the Grote Professor of Mind cluded modern languages and philosophy. Having and Logic at UCL in 1911. This professorship was read some psychology while in India, he resigned eventually (1928) renamed as the “Professorship of his commission in 1898 and at the age of 34 he Psychology”. He was elected as Fellow of the Royal started his graduate training in experimental psy- Society in 1924. Although officially retiring from chology with at the University of UCL in 1931 he continued an active research career Leipzig. Perhaps because of the influence of his for the rest of his life. Always known as gracious army experience, he was less interested in the stud- and thoughtful and exceedingly rational, his death ies of pure (and simple) cognitive and perceptual from a fall from the window of a London hospital processes favored by Wundt, and was more inter- in 1945 is thought to have been his own decision. ested in complex and real life behaviors such as Spearman’s contributions to reliability theory, fac- school achievement. After two years, his graduate tor analysis, and the theory of “g” or general intelli- training was interrupted as he was called back to gence continue to influence psychometric and intel- service in the Boer War where he served on the gen- ligence research more than 100 years later. It may eral staff. Finally, in 1902, he resumed his graduate be said that all of modern psychometrics is merely a training which he completed in 1907. footnote on the work of and Charles An amazing year Spearman is probably most known for two papers he published in the American Journal of Psychology contact: William Revelle [email protected] in 1904 while still in graduate school. Both of these Version of March 1, 2014 papers continue to be cited today with more than To appear in Cautin, R. and Lilienfeld, S (Eds) The Ency- 2,000 citations for each article. Although extraor- clopedia of Clinical Psychology. Wiley-Blackwell dinarily influential and foretelling his eventual ca- This is the submitted LATEXversion and might differ from reer, neither of these papers was related to his even- the final published version. tual dissertation topic on spatial localization. The first introduced reliability and latent trait theory, the 2 PMC LAB second introduced factor analysis and evidence sup- ies (albeit with very small samples of local school porting a theory of the general factor of intelligence. children, local adults, and students at a prestigious The proof and measurement of association be- “public” school). He found that the low intercorre- tween two things (AJP, 1904 pp 72-101) expanded lations of simple cognitive measures with high level on Galton’s idea of the correlation coefficient. Gal- performance measures reflected more the quality of ton’s papers in 1886 and 1888 had introduced his measurement than it did the underlying relation- coefficient of “regression towards mediocrity”, or r, ships. Correcting for unreliability, and in particular, and gave some very good examples of the process correcting for the unreliability within each domain of correlation. Galton’s original insight was then (simple cognitive tasks and academic achievement elaborated by in 1896 into the cor- by finding average domain correlations), Spearman relation that bears his name (the Pearson Product developed the basic principles of factor analysis. Moment Correlation Coefficient). Spearman recog- This was particularly amazing in that it was done nized that the mathematical treatment found in Bra- without the influence of linear or matrix algebra nor vais or Pearson was probably not helpful to most the high speed computing that has made factor anal- psychologists and thus laid out in seemingly very ysis and structural equation modeling such a stan- simple terms the notion of correlation, reliability, dard for quantitative research. and correction for unreliability. Seen from the ad- vantage of a century later, this paper is a master- piece in that it also considers the advantages of a Influence on the field rank order correlation (Pearson r applied to ranked data rather than the raw data) which is more robust Based partly upon these two early papers, Spear- to outliers than is the normal Pearson correlation, man was offered a position at UCL to head the new discusses problems in restriction of range, and gives experimental psychology program there. Over the statistical tests for the probability of any correlation. next 30 years the “London school” of individual dif- The paper also introduces the concept of part and ferences was the home of such scholars are Cyril partial correlation as a way of controlling for ex- Burt, , , and Karl traneous variables. Although many of these ideas Holzinger. Spearman, his students, and his col- had been discussed earlier by Pearson, Spearman’s leagues continued to explore the nature of intelli- clear exposition of the ideas and demonstrations of gence, and his 1927 book, The Abilities of Man best their applications to the study of cognitive perfor- summarizes his two-factor theory of intelligence. mance were very influential for students of individ- As pointed out in ’s biography, Spear- ual differences. His decomposition of an observed man did not view himself as a methodologist, but score into a true score and an error score and the rather a theorist of the nature of cognition. introduction of parallel tests to measure reliability To Spearman, all tests were saturated with gen- are the fundamental statements of what is known as eral intelligence and some specific test variance. classical test theory. Later work, particularly that of Burt, and then The next issue of the American Journal of Psy- Thomson and Thurstone argued against this point chology included Spearman’s second masterpiece: and showed that tests could be grouped into factors “general intelligence,” objectively determined and known as primary mental abilities. However, the measured (AJP, 1904, 201-292) which was a tour de importance of Spearman’s g has seen a revival as force critiquing prior experimental work combined hierarchical models show that the primary abilities with the demonstration of the power of the cor- are actually group factors which in turn can be fac- relation coefficient when corrected for attenuation. tored to produce a second or third order factor that Reviewing earlier studies which failed to find cor- saturates all tests. This is of course, the of relations between experimental measures and rat- Spearman. ings of intelligence, Spearman discussed problems Unlike those of many of his contemporaries, in restriction of range, poorly practiced or unmo- Spearman’s contributions remain very influential to- tivated subjects, and generally poor measurement. day. It is impossible to study psychometrics, test Spearman dismissed some prior studies because of theory, or intelligence without recognizing and pon- these errors, and then reported on his own five stud- dering the work of Charles Edward Spearman. CHARLES E. SPEARMAN 3

See also Spearman, C. (1904a). “General Intelligence,” objec- tively determined and measured. American Journal of Correlational Designs; Eugenics;Hans Eysenck; Psychology, 15(2), 201-292. Francis Galton; Intelligence Testing; Spearman, C. (1904b). The proof and measurement of as- Further Readings sociation between two things. The American Journal of Psychology, 15(1), 72-101. References Spearman, C. (1927). The abilities of man. Oxford Eng- Jensen, A. R. (2000). Charles E. Spearman: The discov- land: Macmillan. erer of g. In G. A. Kimble & M. Wertheimer (Eds.), Portraits of pioneers in psychology (Vol. IV, p. 97- Thomson, G. (1947). Charles Spearman. 1863-1945. 116). Mahwah, N.J.: Lawrence Erlbaum Associates. Obituary Notices of Fellows of the Royal Society, 5(15), 373-385. Lovie, P., & Lovie, A. D. (1996). Charles Edward Spear- man, F.R.S. (1863-1945). Notes and Records of the Royal Society of London, 50(1), pp. 75-88. Retrieved from http://www.jstor.org/stable/531842