As a psychologist, Cattell was rigorously devoted to the scientific method, and was an early proponent of using factor analytical methods instead of what he called "verbal theorizing" to explore the basic dimensions of personality, motivation, and cognitive abilities. One of the most important results of Cattell's application of factor analysis was his discovery of 16 factors underlying human personality. He called these factors "source traits" because he believed they provide the underlying source for the surface behaviors we think of as personality. This theory of 16 personality factors and the instrument used to measure them are known respectively as the 16 Personality Factors and the 16PF Questionnaire.
Although Cattell is best known for identifying the dimensions of personality, he also studied basic dimensions of other domains: intelligence, motivation, and vocational interests. Cattell theorized the existence of fluid and crystallized intelligences to explain human cognitive ability, and authored the Culture Fair Intelligence Test to minimize the bias of written language and cultural background in intelligence testing.
After Cattell had spent almost 7 years of his life in Hilltop, his family moved to Devon, in the south of England, where he grew up with strong interests in science and sailing. He was the first of his family to attend university when in 1921, he was awarded a scholarship to study chemistry at the University of London, where he obtained a magna cum laude BSc at the age of 19. While studying chemistry at university he learned from people of eminence in many other fields, who visited or lived in London. He writes that he:
As he observed first-hand the terrible destruction and suffering from World War I, he was increasingly attracted to the idea of applying the tools of science to the serious human problems that he saw around him. In the aftermath of WWI, he recalled feeling his laboratory bench begin to seem small and the world's problems vast. . Thus, he decided to change his field of study and pursue a Ph.D. in psychology, which he received in 1929.
While working on his Ph.D., Cattell accepted a position teaching and counseling in the Department of Education at Exeter University. During his three years at Exeter, Cattell courted and married Monica Rogers, whom he had known since his boyhood in Devon. In 1932 a son was born to them. Soon after he moved to Leicester where he organized one of England's first child guidance clinics.
After several productive years at Clark, he was invited by Gordon Allport to join the Harvard University faculty in 1941. The three years he spent at Harvard turned out to be a pivotal point in his academic and personal life. While at Harvard he planned and carried out some of the research in personality that would become the foundation for much of his later work in this area.
During World War II, Cattell served as a civilian consultant to the U. S. government developing tests for selecting officers. With the war coming to an end, Cattell married Karen Schuettler, a mathematician who was at Radcliffe College while Cattell was teaching at Harvard. She worked with Cattell on the mathematical and statistical aspects of his research. Three daughters and a son were born to them.
At this time Herbert Woodrow, Professor of Psychology at the University of Illinois at Urbana-Champaign and President of the APA, was searching for someone with a background in multivariate methods to establish a research department. Cattell was invited to assume this position in 1945 and he accepted. In this newly created professorship in psychology he was able to obtain sufficient grant support for two Ph.D. associates, four graduate research assistants, and clerical assistance each year for nearly 30 years.
It was his good fortune that physicists at the University of Illinois were developing an electronic computer, the Illiac I, which would make it possible for him to undertake large-scale factor analyses. In 1949 he and his wife, Karen Cattell, founded The Institute for Personality and Ability Testing (IPAT). Karen served as director and chairperson of IPAT until 1992. Cattell also founded the Laboratory of Personality Assessment and Group Behavior which initiated a period of remarkable creativity with a talented staff of research associates coming from all over the world.
In 1960, Cattell was instrumental in convening an international symposium to increase communication among researchers using multivariate statistics to study human behavior; this resulted in the foundation of the Society of Multivariate Experimental Psychology. Cattell's time at Illinois was one of prodigious productivity. The sheer number of talented researchers from many places around the globe, whom he invited or influenced, was extraordinary. His books are filled with lengthy lists of co-workers who contributed to his program of research. He would also continue to collaborate with them long after they left his laboratory. He remained in the Illinois research professorship until he was required to retire in 1973, because of University age regulations then in place. Largely due to Cattell, the University of Illinois in Champaign-Urbana became the world's most productive center for multivariate experimental psychology. After he retired from the University of Illinois he relocated to Boulder, Colorado for 5 years, where he published the results of a variety of research projects that had been left unfinished in Illinois.
In 1978 he decided to take up residence in Hawaii and began another career as professor and advisor at the University of Hawaii. Subsequently he joined the Hawaii School of Professional Psychology, which became the American School of Professional Psychology. Upon settling in Hawaii he married Heather Birkett, a clinical psychologist, who has carried out extensive research using the 16PF and other tests. During the last 2 decades of his life in Hawaii, Cattell continued his productive pace, publishing a variety of scientific articles, as well as books on morality, motivation, the scientific use of factor analysis, two volumes of personality and learning theory, the inheritance of personality and ability, intelligence, structured learning theory; and co-edited a book on functional psychological testing, as well as a revision of his Handbook of Multivariate Experimental Psychology. Then:

Cattell also found that concepts used by early psychological theorists tended to be subjective and poorly defined. For example, after examining over 400 published papers on the topic of anxiety in 1965, Cattell stated "The studies showed so many fundamentally different meanings used for anxiety and different ways of measuring it, that the studies could not be integrated.”. Early psychologists also tended to provide little objective evidence or research on their theories. Cattell wanted psychology to become more like medicine and other sciences, where a theory could be tested in an objective way that could be replicated by others. In Cattell's words:
During the remainder of his career, he steadfastly pursued this goal, advancing the scientific approach to psychology. Psychologist Art Sweney, an expert in psychometrics, summed up Cattell’s methodology:

Cattell used multivariate research to explore, identify, and understand the basic, underlying elements of human behavior in three domains: the traits of personality or temperament, the motivational or dynamic traits, and the diverse dimensions of abilities. In each of these areas, he thought there must be a finite number of basic, unitary, elements that could be identified. He drew a comparison between these fundamental, underlying traits to the basic elements of the physical world that were discovered and presented in the periodic table of the elements.
In his research, Cattell reached out to psychologists around the world to cooperate in using a multivariate approach. In 1960, he organized an international meeting of research-oriented psychologists, which resulted in the founding of the Society for Multivariate Experimental Psychology, and its journal, Multivariate Behavioral Research. Cattell collaborated with dozens of psychologists around the world on a broad spectrum of research projects. He brought many of these talented researchers from Europe, Asia, Africa, Australia, and South America to work at his lab at the University of Illinois. Many of his influential books were written in collaboration with others.
Factor analysis was built upon the earlier development of the correlation coefficient, which measures whether two variables are related or tend to go together. For example, if frequency of exercise and blood pressure level were measured on a large group of people, then intercorrelating these two variables will indicate to what degree exercise and blood pressure are directly related to each other. Factor analysis performs complex calculations on the correlation coefficients among a multitude of variables in a particular domain (such as abilities or personality) to determine the basic, unitary factors at work behind the superficial variables in that domain.
While working at the University of London with Spearman exploring human abilities, Cattell postulated that factor analysis could be applied to other areas beyond the domain of abilities. In particular, Cattell was interested in exploring the basic dimensions and structure of human personality. For example, he thought that if factor analysis were applied to a wide range of measures of interpersonal functioning, the basic dimensions within the domain of social behavior could be identified. Thus, factor analysis could be used to discover the fundamental dimensions behind the large number of apparent surface behaviors and then facilitate more effective research in this area.
In order for a personality dimension to be called “fundamental and unitary,” Cattell believed that it needed to be found in factor analyses of data from all three of these domains. Thus, Cattell constructed personality measures of a wide range of traits in each medium. He then repeatedly performed factor analyses on the data.
With the help of many colleagues, Cattell's factor-analytic studies continued over several decades, eventually producing 16 fundamental factors underlying human personality. He decided to name these traits with letters (A, B, C, D, E…), like vitamins, in order to avoid misnaming these newly discovered dimensions, or inviting confusion with existing vocabulary and concepts. Factor-analytic studies by many researchers in diverse cultures around the world have re-validated the number and meaning of these traits. This international confirmation and validation established Cattell’s 16 factors as objective and scientific.
Cattell set about developing tests to measure these traits across different age ranges, such as The 16 Personality Factor Questionnaire for adults, the Adolescent Personality Questionnaire, and the Children’s Personality Questionnaire. These tests have now been translated into many languages and validated across different cultures.
After discovering these 16 primary level factors, Cattell reasoned that, as in other scientific domains, there might be an additional, higher level of organization within personality which would provide a structure for the many primary traits. When he factor analyzed the 16 primary traits themselves, he found five “second-order” or global factors, now commonly known as the Big Five . These second-order or global traits were broad, over-arching domains of behavior, which provided meaning and structure for the primary traits. For example, the global trait Extraversion emerged from factor-analytic results which loaded the five primary traits that were interpersonal in focus.
Thus, global Extraversion is fundamentally related to the primary traits that came together in the factor analysis to define it, and the domain of Extraversion gave conceptual structure to these primary traits, identifying their focus and function. These two levels of personality structure can be used to provide an integrated understanding of the whole person, with the global traits giving an overview of the individual’s functioning in a broad-brush way, and the more-specific primary trait scores providing an in-depth, detailed picture of the individual’s unique trait combinations.
Research on the basic 16 traits has found them useful in understanding and predicting a wide range of real life behaviors. For example, the traits have been used in educational settings to study and predict such things as achievement motivation, learning style or cognitive style, creativity, and compatible career choices; in work or employment settings to predict such things as leadership style, interpersonal skills, conscientiousness, stress-management, and accident-proneness; in medical settings to predict heart attack proneness, pain management, likely compliance with medical instructions, or recovery pattern from burns or organ transplants; in clinical settings to predict self-esteem, interpersonal needs, frustration tolerance, and openness to change; and, in research settings to predict a wide range of dimensions such as aggression, conformity, and authoritarianism.
Cattell’s comprehensive program of personality research in the 1940’s, 50’s, and 60’s resulted in five books that have been widely recognized as identifying fundamental dimensions of personality and their organizing principles:
These books detailed a program of research that was theoretically comprehensive and methodologically sophisticated, bringing together personality data from objective behavioral studies, from self-report or questionnaire data, and from observer ratings. They presented a theory of personality development over the human life span, including effects on the individual’s behavior from family, social, cultural, biological, and genetic influences, as well as influences from the domains of motivation and ability. These books have been widely referenced, and fundamentally influenced the development of scientific psychology.
In 1994, Cattell was one of 52 signatories on "Mainstream Science on Intelligence," an editorial written by Linda Gottfredson and published in the Wall Street Journal, which defended the findings on race and intelligence in The Bell Curve. In 1997, Cattell, at 92, was chosen by the American Psychological Association (APA) for its "Gold Medal Award for Lifetime Achievement in the Science of Psychology." However before the medal was presented, a former student at the University of Illinois, Barry Mehler, launched a publicity campaign against Cattell
through his nonprofit foundation ISAR accusing Cattell of being sympathetic to racist and fascist ideas
and claiming that "it is unconscionable to honor this man whose work helps to dignify the most destructive political ideas of the twentieth century".
A blue-ribbon committee was convened by the APA to investigate the legitimacy of the charges. However, before the committee reached a decision, Cattell issued an open letter to the committee saying "I abhor racism and discrimination based on race. Any other belief would be antithetical to my life’s work" and saying that "it is unfortunate that the APA announcement … has brought misguided critics' statements a great deal of publicity."
He refused the award, withdrawing his name from consideration. The blue ribbon committee was therefore disbanded and Cattell, in failing health, died months later.