W. W. Norton & Company | The Personality Puzzle, 4th ed.

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Chapter 2: Clues to Personality: The Basic Sources of Data

In order to study personality, first you must look at it: all science begins with observation. The observations a scientist makes are called data.

For the scientific study of personality, four types of data are available. Each type has advantages and disadvantages.

S or "self-judgment" data comprise a person's assessments of his or her own personality. The advantages of S data are that each individual is the best expert about herself or himself, that S data also have a causal force all their own, and that S data are simple and easy to gather. The disadvantages are that people sometimes will not or cannot tell researchers about themselves, and that S data may be so easy to obtain that psychologists rely on them too much.

I or "informant" data comprise the judgments of knowledgeable acquaintances about the personality traits of the person being studied. The advantages of I data include the large amount of information on which informants' judgments typically are based, that this information comes from real life, that informants can use common sense, and that the judgments of people who know the person are important because they affect reputation, opportunities, and expectancies. The disadvantages of I data are that no informant knows everything about another person, that informants' judgments can be biased or subject to errors such as forgetting, and that not all informants may have common sense.

L or "life" data comprise observable life outcomes such as being arrested, getting sick, or graduating from college. L data have the advantages of being intrinsically important and potentially psychologically relevant, but they have the disadvantage of not always being psychologically relevant.

B or "behavioral" data comprise direct observations of a person doing something in a testing situation. This situation may involve the person's real-life environment, an artificial social setting constructed in a psychological laboratory, a personality test such as the Rorschach inkblot, or a physiological measurement of variables such as heart rate, blood pressure, and even brain activity. The advantages of B data are that they can tap into many different kinds of behaviors, including those that might not occur or be easily measured in normal life, and that B data are obtained through direct observation, and so are in that sense objective. The disadvantage of B data is that for all their superficial objectivity, it is still not always clear what they mean psychologically.

Because each kind of data for personality research is both potentially valuable and potentially misleading, discrepancies among data sources can be as informative as agreement between them. Therefore, researchers should gather and compare as many different types of data as possible.