Final answer:
Personality researchers Raymond Cattell and Hans Eysenck used factor analysis to determine important personality traits.
Step-by-step explanation:
Personality researchers Raymond Cattell and Hans Eysenck both used factor analysis to determine the important personality traits. Factor analysis is a statistical method that identifies underlying dimensions, or factors, that explain the correlations among a set of observed variables. By analyzing the relationships between different traits, Cattell and Eysenck were able to identify and categorize important personality factors.