According to Hans Eysenck and Sybil Eysenck, the individual variation that is apparent across people can be reduced to several dimensions, including:

Answer: Extraversion-introversion

Explanation: These two Eysenck psychologists were personality theorists, and their theory is based on inborn traits, more precisely on differences of personalities that are genetic and therefore inborn. They took a biological approach to the study of personality, believing that biological predispositions largely determine personality. The sphere of their scientific interest and research are two dimensions of higher order traits, which are extraversion versus introversion. In addition, the dimension of emotional stability versus emotional instability is also a dimension of higher order traits. Thus, those differences that appear in personality are reduced to several higher order dimensions, of which these two are mentioned here. It should be noted that these scholars also focused on personality temperament when studying personality differences and on temperament also based their claims on genetic predispositions. On this basis, they developed a questionnaire for determining personality type and according to this questionnaire there are four personality scales.