Louis L. Thurstone, who spent most of his career at the University of Chicago before founding a major psycho-metric lab at the University of North Carolina, made significant contributions to psychometrics, statistics, and the study of human intelligence during his long career. Thurstone developed methods for scaling psychological measures, assessing attitudes, and test theory, among many other influential contributions. In statistics, he is best known for the development of new factor analytic techniques to determine the number and nature of latent constructs within a set of observed variables.
These new statistical techniques allowed Thurstone to make his most enduring contribution to psychology: the theory of primary mental abilities, a model of human intelligence that challenged Charles Spearman’s then-dominant paradigm of a unitary conception of intelligence. Spearman, using an earlier approach to factor analysis, found that scores on all mental tests (regardless of the domain or how it was tested) tend to load on one major factor. Spearman suggested that these disparate scores are fueled by a common metaphorical “pool” of mental energy. He named this pool the general factor, or g.
Thurstone argued that g was a statistical artifact resulting from the mathematical procedures used to study it. Using his new approach to factor analysis, Thurstone found that intelligent behavior does not arise from a general factor, but rather emerges from seven independent factors that he called primary abilities: word fluency, verbal comprehension, spatial visualization, number facility, associative memory, reasoning, and perceptual speed. Furthermore, when Thurstone analyzed mental test data from samples comprising people with similar overall IQ scores, he found that they had different profiles of primary mental abilities, further supporting his model and suggesting that his work had more clinical utility than Spearman’s unitary theory.
However, when Thurstone administered his tests to an intellectually heterogeneous group of children, he failed to find that the seven primary abilities were entirely separate; rather, he found evidence of g. Thurstone managed an elegant mathematical solution that resolved these apparently contradictory results, and the final version of his theory was a compromise that accounted for the presence of both a general factor and the seven specific abilities. Thurstone’s 1934 presidential address to the American Psychological Association provides a good overview of his work in the fields of statistics, intelligence, and psychometrics.
Although g-centric theories based on Spearman’s work remain popular in the 21st century, Thurstone’s theoretical and statistical work laid the groundwork for the development of well-regarded hierarchical theories of intelligence, such as those proposed by John Horn and Raymond Cattell, J. P. Guilford, and John Carroll. Thurstone’s work also provided the theoretical and statistical foundations for many of the most highly respected tests of cognitive ability currently in use, including the Wechsler intelligence scales and the Armed Forces Vocational Aptitude Battery.
References:
- Ruzgis, P. (1994). Thustone, L.L. (1887-1955). In R. J. Sternberg (Ed.), Encyclopedia of human intelligence (pp. 1081-1084). New York: Macmillan.
- Thurstone, L. L. (1934). The vectors of mind. Psychological Review, 41, 1-32. Retrieved May 31, 2016, from http://psychclassics.yorku.ca/Thurstone/
- Thurstone, L. L. (1938). Primary mental abilities. Chicago: University of Chicago Press.
- Thurstone, L. L. (1952). L. L. Thurstone. In E. G. Boring, H. S. Langfeld, H. Werner, & R. M. Yerkes (Eds.), A history of psychology in autobiography (Vol. 4, pp. 295-321). Worcester, MA: Clark University Press.