sychometry has dominated intelligence for over a century now. Sounds quite profound, right? Especially considering the many paradox introduced with it. In simple words, psychometrics is a scientific field of psychology, concerned with the creation of theoretical models and assessment tools that serve to associate observable phenomena with theoretical attributes.
Theories have been developed for over a century now with the aim to improve our understanding of the structure of human intelligence. As the defining feature of this approach suggests, these theories refer to the quantitative assessment of one’s psychological abilities or so-called mental capacity. They are based on a model that serves to portray intelligence as a composite of one’s abilities including analogies, classifications, and series completions.
One of the early theories was developed by the psychologist of British origin, Charles E. Spearman (1863–1945), who published his first major article on the topic of human intelligence in 1904. He developed a statistical technique, namely “factor analysis”, that allows psychologists to assess one’s common abilities through a set of tests. Different associations and/ or correlations may arise from the database of these tests. For example, based on test results it can be identified that individuals who perform well on questions that assess vocabulary performance also perform better on questions related to reading comprehension.
Spearman concluded that the difference in test scores of individuals whose psychological abilities have been assessed was underlined by two key factors. He labeled these factors – “general factor” (known as g), and the test-specific factor which is dependent upon the specifics of the particular test that the subject of testing has undergone. Thus, while g, is a set factor that pervades performance on all tasks requiring intelligence, regardless of the nature of the task, the test-specific factor changes corresponding to the set demands of the test itself. However, it is believed that Spearman wasn’t himself aware of what the general factor was, until 1927 when he proposed that it might be “mental energy”, yet leaving it undefined. [Keep this one in mind for now, please].
Contradicting Spearman’s theory, L.L. Thurstone came out with the idea that the difference in test scores was dependent upon seven factors, collectively identified as the “primary mental abilities”. These seven abilities, according to Thurstone, were verbal comprehension, verbal fluency, number, spatial visualization, inductive reasoning, memory, and perceptual speed.
Although the debate between the two big names in psychometrics remained unresolved, the work of other psychologists including Philip E. Vernon and Raymond B. Cattell was based on the foundation of the early developed theories. And so, Vernon and Cattell viewed intellectual abilities as hierarchical with g taking its rightful place at the top of the hierarchy. Down the hierarchy they placed gradually narrowing abilities, ending with the findings of Spearman.
In his later work, Cattell proposes that general ability can be subdivided into two further kinds, “fluid” and “crystallized” (Abilities: Their Structure, Growth, and Action (1971). The fluid abilities, for those wondering, are considered the reasoning and problem-solving abilities which are generally assessed by tests such as analogies, classifications, and series completions. Whereas Crystallized abilities that are said to be a by-product of fluid abilities include vocabulary, general information, and knowledge about specific fields [such as Psychometrics, exciting, isn’t it?]. To add further value, the American psychologist John L. Horn proposed that crystallized abilities increase over one’s life span, whereas fluid abilities increase in earlier years and decrease in later ones [remember the curves from school mathematics? if the gradient of the tangent is positive, then the function is increasing and if the gradient is negative then the function is decreasing].
To add further complexity I will also briefly mention the “ three-stratum” psychometric model of intelligence that resulted from the existing theories of intelligence, as introduced by the American psychologist John B. Carroll, in Human Cognitive Abilities (1993). The three-layered model suggests gradation, with each layer accounting for the variations in the correlations within the previous layer to produce a scheme showing the differences among individuals in their performance, in a stable and observable way.
In essence, his model serves as a proposition that intelligence is conceptualized in a hierarchy of three strata: Stratum III (general intelligence and narrow abilities, including the seven primary abilities identified by Thurstone), Stratum II (broad abilities such as learning, retrieval ability, speediness, visual perception, fluid intelligence, and the production of ideas) & Stratum I (individual-specific intelligence).
And so, many new-generation psychologists think of Carroll’s model as definitive, considering its strong foundation in datasets analyses. It all makes sense now, right? Mathematics meets psychology and here comes psychometrics. If it does so, then it’s time to make it slightly less interpretable, asking the question we all had in mind at the top of this paper…
It does seem self-evident that Spearman’s general factor is to be placed at the top of the hierarchy since it is individual-specific, yet there is still little to no guarantee of its existence. It can be therefore argued that we are now exploring the foundations of a theory-based field that has the potential to serve as a reliable measure of human personality, abilities, aptitude, and interests. Thus, it is in the hands of the future generation of psychometric theorists to find out more about g’s existence and to further expand and enrich the knowledge and understanding we have of psychometric evaluation and individual assessment.
“I exist here, now. I’m not much interested in the future. Or, more precisely put, I do not believe in the future. To exaggerate a little, I have no faith that I will still exist tomorrow or the day after. What is more, I absolutely detest retrospection. That dislike is balances only by my desire to make my way back home as quickly as possible.”– Yohji Yamamoto