Factor analysis
Assumptions shared by standardized personality tests, simply stated, are that humans possess characteristics or traits that are stable, vary from individual to individual, and can be measured. Factor analysis is a statistical procedure for reducing the redundancy in a set of intercorrelated scores. One major technique of factor analysis, the principal-components method, finds the minimum number of common factors that can account for an interrelated set of scores. Cattell's goal was to empirically determine and measure the essence of personality. Cattell used factor analysis to reduce thousands of psychological traits into what he believed to be 16 of the basic dimensions, or source traits of human personality. As a result, he created the 16PF personality test.