Raymond Bernard Cattell (20 March 1905 - 2 February 1998) was a British and American psychologist, known for his psychometric research into intrapersonal psychological structure. His work also explored the basic dimensions of personality and temperament, the range of cognitive abilities, the dynamic dimensions of motivation and emotion, the clinical dimensions of abnormal personality, patterns of group syntality and social behavior, applications of personality research to psychotherapy and learning theory, predictors of creativity and achievement, and many multivariate research methods including the refinement of factor analytic methods for exploring and measuring these domains. Cattell authored, co-authored, or edited almost 60 scholarly books, more than 500 research articles, and over 30 standardized psychometric tests, questionnaires, and rating scales. According to a widely cited ranking, Cattell was the 16th most eminent, 7th most cited in the scientific journal literature, and among the most productive, but controversial psychologists of the 20th century.

Cattell noted that in the hard sciences such as chemistry, physics, astronomy, as well as in medical science, unsubstantiated theories were historically widespread until new instruments were developed to improve scientific observation and measurement. In the 1920s, Cattell worked with Charles Spearman who was developing the new statistical technique of factor analysis in his effort to understand the basic dimensions and structure of human abilities. Factor analysis became a powerful tool to help uncover the basic dimensions underlying a confusing array of surface variables within a particular domain.  Factor analysis was built upon the earlier development of the correlation coefficient, which provides a numerical estimate of the degree to which variables are "co-related". For example, if "frequency of exercise" and "blood pressure level" were measured on a large group of people, then intercorrelating these two variables would provide a quantitative estimate of the degree to which "exercise" and "blood pressure" are directly related to each other. Factor analysis performs complex calculations on the correlation coefficients among the variables within a particular domain (such as cognitive ability or personality trait constructs) to determine the basic, unitary factors underlying the particular domain.  While working at the University of London with Spearman exploring the number and nature of 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 taxonomic dimensions and structure of human personality. He believed that if exploratory 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 underlying the large number of surface behaviors, thereby facilitating more effective research.  As noted above, Cattell made many important innovative contributions to factor analytic methodology, including the Scree Test to estimate the optimal number of factors to extract, the "Procrustes" oblique rotation strategy, the Coefficient of Profile Similarity, P-technique factor analysis, dR-technique factor analysis, the Taxonome program, as well the Rotoplot program for attaining maximum simple structure solutions. In addition, many eminent researchers received their grounding in factor analytic methodology under the guidance of Cattell, including Richard Gorsuch, an authority on exploratory factor analytic methods.Answer this question using a quote from the following article:

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then intercorrelating these two variables would provide a quantitative estimate of the degree to which "exercise" and "blood pressure" are directly related to each other.