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PERSONALITY ASSESSMENT: EFFECT SIZE, REPLICABILITY, AND OPEN SCIENCE

Chapter Opener. A man is in focus, and he is walking down a sidewalk. There is a woman trying to hand him a sheet of paper. Behind them stands another individual next to a banner for Scientology.

If something exists, it exists in some quantity, and if it exists in some quantity, it can be measured.

—EDWARD LEE THORNDIKE

ARE YOU MORE OR LESS extraverted than the person sitting next to you? Are you more or less conscientious? To decide who is the most extraverted or conscientious person in the room, or, more broadly, for personality traits to be useful for the scientific understanding of the mind, the prediction of behavior, or for any other purpose, the first step is measurement. The previous chapter considered several methods used by personality research. This chapter begins by more closely considering the methods used for personality assessment. But personality assessment—like psychological research more generally—itself needs to be assessed. Evaluating how well “personality tests” predict behavior, as well as evaluating the strength of any research result, requires understanding measures of effect size and evidence concerning replicability. These two topics are addressed in the second part of this chapter. Finally, the third part of this chapter considers the ethics of personality research. Ethical issues include how personality assessments are used, how research participants are treated (and how they must be protected), and the ways in which personality research—and scientific research more generally—is and should be conducted.