Psychology became a comparatively “harder” science when it embraced psychometrics, a mathematically focused branch of psychology for objective measurement.
Psychology became a comparatively “harder” science when it embraced psychometrics, a mathematically focused branch of psychology for objective measurement.
This quantitative approach not only measures intelligence and personality, but also applies statistical methods to improve the accuracy of psychological testing.
Psychometrician Henk Kelderman noted that psychometric models are widely applied in “education, industrial and organizational psychology, behavioral genetics, neuropsychology, clinical psychology, medicine, and even chemistry” (Psychometric Society, 2022).
Today, psychometric testing is used globally by major companies, among other businesses, during the hiring or development process. If you’ve never heard of psychometrics, you might wonder why it is popular now, and where it is headed. But in order to know where something is going, you need to know where it came from.
The coining of the term psychometric(s), along with the original definition, can be traced back to the year 1879. Francis Galton, the British scientist who also developed the first newspaper weather map, defined psychometry as “the art of imposing measurement and number upon operations of the mind” (Galton, 1879. p. 149). Galton studied his own mental associations, specifically when their formation began in the lifespan, the rate they were created at, their salience, and how often they recurred. In essence, Galton took something that was once illusory and phantasmal—the mental operations of the mind—put it down on paper with a number value, and compared the results statistically.
However, there is another person with a legitimate claim to the fathership of psychometrics. William James Cattell, a student of Wilhem Wundt, became the first American to publish a dissertation, titled Psychometric Investigation (1886), in experimental psychology (Baron, 2006). Catell founded the first psychometric lab in 1887, within the Cavendish Physics Laboratory at the University of Cambridge (Cattell, 1928). Further, Catell coined the term mental tests in 1890 to describe a series of psychological tests that involved mental measurements such as:
For example, in the time judgment test, Cattell would strike the table with a pencil, and then again after 10 seconds had elapsed—as measured by a watch. Then the participant would strike the desk with a pencil after they believed that another 10 seconds had passed (Cattell, 1890).
Cattell even worked in Galton’s lab; the pair had a passion for measuring individual differences. But by the turn of the century, a different group of scientists would give new meaning to the term psychometrics, all in the pursuit of measuring human intelligence.
In 1904 Charles Spearman coined perhaps the most famous measure of intelligence and psychometrics, general intelligence (g). After correlating the test scores of children between various items, Spearman realized that performance was generally consistent. In other words, children who performed well on a given test item—say verbal ability—would score similarly on other subjects—say mathematics—even though the two subjects are not necessarily related. On the other end, poor performers generally…well…performed poorly.
Spearman analyzed these results, and concluded that a single mental faculty, general intelligence (g), could explain performance on any mental task (Spearman, 1904). Additionally, Spearman noted that each mental test contained a test-specific factor, called (s). For example, when you solve a reading and comprehension problem, you use (g) because the test measures intelligence. In addition to (g), you also use specific mental abilities specifically related to reading and comprehension.
More critically, with Spearman’s conception of (g), factor analysis was born. This statistical method is still widely used in psychometric testing.
Only a calendar year after Spearman’s findings on general intelligence, Alfred Binet and Theodore Simon published a new test for measuring intelligence called the Binet-Simon scale (1905). Binet set out to measure a child’s intelligence through a subject's attention, judgment, knowledge, and memory. In doing so, Binet created the first intelligence test.
In 1908, the first revision of the scale put forth the concept of mental level. If you perform lower than another person your age, you have a lower mental level. If you over perform, then you have a higher mental level. In fact, the Binet-Simon scale was so brilliant that a Stanford psychologist decided to beef it up and make it his own.
In 1916, Lewis Terman released the Stanford-Binet intelligence scales. Terman wanted to create a test that could be normally distributed for the purposes of educational placement. The revised version of the Binet-Simon scale added more tests and increased the age range in the normative sample (Minton, 1998). For a period of time, Terman’s test calculated intelligence quotient (IQ) through a now famous formula: IQ = mental age/chronological age x 100.
The first World War saw a veritable rise in psychometric testing—led by then president of the American Psychological Association (APA) Robert Yerkes—resulting in a large database of psychometric information (Jones and Thissen, 2007). Charles Brighman, who analyzed the data and published the results in the book A Study of American Intelligence, would go on to create the Scholastic Aptitude Test (SAT) in 1926 (Schonemann, 2006).
The Psychometric Society was founded in 1935 in Ann Arbor, Michigan by L.L. Thurstone, who created the world’s first attitude scale (Jones and Thissen, 2007). The society’s official journal, Psychometrika, released its first publication in the following year. Now over 80 years old, the Psychometric Society upholds its mission to advance the quantitative measurement practices of psychology.
Thurstone, another influential figure in psychometrics, disagreed with Spearman’s “two-factor theory.” He argued that a) Spearman’s method was actually just a single factor theory revolving around general intelligence, and (b) there were seven primary factors, which Thurstone developed in his multiple factor analysis (Thurstone, 1934 1938, 1947). The seven primary “mental abilities” consisted of associative memory, general reasoning, number ability, perceptual speed, spatial ability, verbal comprehension, and word fluency.
A 2021 survey from the past 20 presidents of the Psychometric Society—published in Psychometrika—highlighted two other major influences in the history of psychometrics: Lee Cronbach and the duo of Lord and Novick.
Lee Cronbach, former president of the American Psychological Association (APA), is widely known for his work on the reliability coefficient called Cronbach’s alpha, a staple in modern testing for measuring internal consistency. Cronbach also proposed a Generalizability theory of reliability (1963). Cronbach built on the classical test theory (CTT) by creating a more flexible approach for measurement that accounted for errors introduced by different test types and the testing environment. One former president said of Cronbach, “he laid down some real mile-posts, about how psychometrics is not just about measurement, it is about the quality and the nature of inferences that you’re making” (Wijsen and Borsboom, 2021, p. 331).
The 2021 survey’s most common answer to the question of the most significant piece of work in the history of psychometrics was Lord and Novick’s 1968 book titled Statistical theories of mental test scores. During a transitional time where psychometrics shifted from the classical test theory (CTT) to modern ones like the item response theory (IRT), Lord and Novick detailed both topics in such a way that marked the “paradigm shift in psychometrics” (Wijsen and Borsboom 2021, p. 330). This transition would carry IRT to its heights through the 1970s and early 1980s.
20th century psychometrics culminated in the test linking movement, an effort to reduce the amount of time spent taking the numerous educational achievement tests of the time (Jones and Thissen, 2007).
According to the past presidents of the Psychometric Society, it looks like the field is here to stay, for now. While some presidents worry about falling behind the rapid advances in technology, others see it as an opportunity. As Ulf Böckenholt said, “We live in the age of big data, the age of self-quantification. I carry a Fitbit. It is the dream of the psychometrician” (Wijsen and Borsboom, 2021, p. 338).
Now, more than ever, the global society is obsessed not only with measurement, but also with maximizing performance by matching people with skills to organizations that need to fill them. As interests in education and job performance continue to rise, so will the need for psychometricians.
After all, where there are tests being developed, there should be psychometricians present to make sure that everything is reliable and fair.
References:
Baron, J. (2006). Catell at Penn. UPenn Psych History.
Binet, A., Kite, E. (1905, 1916). New Methods for the Diagnosis of the Intellectual Level of Subnormals. L'Année Psychologique, 12. pp. 191-244.
Brigham, C. C. (1923). A study of American intelligence. Princeton University Press.
Cattell, J. M. (1890). V.-Mental tests and measurements. Mind, 15. pp. 373-381.
Cattell, J. M. (1928). Early psychological laboratories. Science, 67(1744). pp. 543–548.
Cronbach, L. J., Rajaratnam, N., & Gleser, G. C. (1963). Theory of generalizability: A liberalization of reliability theory. British Journal of Statistical Psychology, 16(2). pp. 137–163.
Galton, F. (1879). Psychometric experiments. Brain: A Journal of Neurology. pp. 149-162.
Jones, L.V., Thissen, D. (2006). 1 A History and Overview of Psychometrics. Handbook of Statistics, 26. pp. 1-27.
Lord, F.M., Novick, M.R., & Birnbaum, A. (1968). Statistical theories of mental test scores. Addison-Wesley.
Minton, H. (1998). Introduction to: "The uses of intelligence tests Lewis M. Terman (1916).
Schonemann, P. (2005). Psychometrics of intelligence. Encyclopedia of Social Measurement. pp. 193-201
Spearman, C. (1904). “General Intelligence,” Objectively Determined and Measured. The American Journal of Psychology, 15(2). pp. 201–292.
Terman, L. M. (1916). The measurement of intelligence. Houghton, Mifflin and Company.
Thurstone, L. L. (1934). The vectors of mind. Psychological Review, 41(1). pp. 1–32.
Thurstone, L.L. (1938). Primary mental abilities. University of Chicago Press: Chicago.
Thurstone, L.L. (1947). Multiple factor analysis. University of Chicago Press: Chicago.
Wijsen, L. D., Borsboom, D. (2021). Perspectives on Psychometrics Interviews with 20 Past Psychometric Society Presidents. Psychometrika, 86(1). pp. 327–343.
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