Personality research with non-human primates: theoretical formulation and methods.

Since the earliest periods of primatology study, researchers have been aware of animals' consistent individual differences in behavior or personality. Many papers have been published on this subject, but they lacked a common theoretical and methodological background. The present work is an attempt to provide such theoretical and methodological foundations to this field of biological science. In the theoretical formulation section, "biological study of personality" is first derived as an extension of the ethology paradigm, and non-human primate personality research is subsequently characterized as its strategic component. In the methodology section, brief reviews and discussions are presented on subjective and objective personality assessment methods with non-human primates with a reference to the reliability and validity concepts in human psychometrics. The work provides a theoretical framework and methodological suggestions for non-human primate personality research.