Experimental Approaches to the Study of Personality William Revelle Northwestern University Abstract A review of the use of experimental techniques to develop and test theories of personality processes. Threats to valid inference including problems of scaling, reliability, and unintended confounds are considered. Basic experi- mental designs are discussed as ways of eliminating some, but not all threats to validity. A number of basic analytical procedures are demonstrated using simulated data that can be accessed from the web based appendix. Personality is an abstraction used to explain consistency and coherency in an indi- viduals pattern of affects, cognitions, desires and behaviors. What one feels, thinks, wants and does changes from moment to moment and from situation to situation but shows a patterning across situations and over time that may be used to recognize, describe and even to understand a person. The task of the personality researcher is to identify the consistencies and differences within and between individuals (what one feels, thinks, wants and does) and eventually to try to explain them in terms of set of testable hypotheses (why one feels, thinks, wants and does). Personality research is the last refuge of the generalist in psychology: it requires a familiarity with the mathematics of personality measurement, an understanding of genetic mechanisms and physiological systems as they interact with environmental influences to lead to development over the life span, an appreciation of how to measure and manipulate affect and cognitive states, and an ability to integrate all of this into a coherent description of normal and abnormal behavior across situations and across time. Although the study of personality is normally associated with correlational tech- niques relating responses or observations in one situation or at one time with responses in other situations and other times, it is also possible to examine causal relations through To appear in Personality Research Methods B. Robins, C. Fraley and R. Krueger, eds Guilford, 2007 address comments to revelle@northwestern.edu