Personality Psychology as an empirical science examines relatively stable individual differences in human experiences and behavior as well as underlying structures and processes. These individual differences characterize the individual's personality during a certain period of life; long term personality changes are not excluded. Their examination is conducted by comparison of individuals (interindividual differences) or groups within a certain population (group differences, such as gender differences). Thereby, detailed descriptions of individual cases (idografic approach) and extensive comparison of different individuals (differential approach) have to be balanced. Personality Psychology primarily deals with norm characteristics of individual differences and their relationship with clinical characteristics, the latter being subject to Clinical Psychology. Examining personality also includes individual differences in genes, anatomy and physiology of the nervous system, as well as individual differences in environment.