1. The Moderator Approach to Personality: When Do Traits Predict Behavior Well, and When Don’t They?

2. Theoretical issues
Traits capture relatively stable individual differences.
Traits are assumed to be relatively stable over time.
Traits are also assumed to be relatively stable across situations.
Person-situation interactions can also occur.
Aggregation is important in capturing the kind of larger, more representative sample of behavior that traits have the best chance to predict.

3. Assumption 1: There are meaningful differences between individuals
There are meaningful differences between individuals (trait psychology is also called differential psychology)
People differ in the degree to which they possess traits, and these differences can be accurately measured.
According to trait psychologists, every person can be characterized in terms of his or her relative standing on a set of human trait dimensions.

4. Assumption 2: Personality results in some degree of consistency over time
Research indicates consistency over time for broad traits, particularly temperament-relevant traits with high heritabilities.
Although consistent over time, how a trait is manifested in behavior might change over time.
How can there be consistency in a trait if it is known to change with age (e.g., impulsivity)? Focus on the rank order differences between people, aggregated across both time and situations.

5. Assumption 3: Personality results in some degree of consistency across situations
Trait psychologists traditionally assumed cross-situational consistency.
However, in the 1970s, people who called themselves situationists argued that behaviors vary in response to one’s changing situations and that there is little evidence for cross-situational consistency based on traits.
For example, Hartshorne and May (1928) found low cross-situational consistency in schoolchildren’s traits of honesty, helpfulness, and self-control.
If situations mainly control how people behave, then the relevance―and even the very existence―of traits is questionable.

6. The situation versus trait controversy: Walter Mischel’s criticisms of the trait approach
Trait measures do not predict relevant behavioral measures well (the presumed .30 to .40 upper range of trait-based prediction).
There is little evidence for cross-situational consistency. Behavior reveals more situational specificity than most trait theorists suggest.
The predictive validity of trait measures does not justify their use in making important decisions about people (e.g., diagnosis and hiring decisions).

7. Mischel’s (1968) pessimistic conclusions
Mischel (1968): Personality psychologists should abandon their efforts to explain behavior with traits, focusing instead on situations.
Situationism: If behavior varies across situations, then situational differences, and not personality traits, determine behavior.

8. Three categories of moderating variables in personality research (Snyder & Ickes, 1985)
Category
Function
Representative Examples
Situational moderating variables
Specify in which types of situations traits will be good versus poor predictors of their trait-relevant behaviors
Psychologically weak versus strong situations
Precipitating versus non-precipitating situations
Personal moderating variables
Specify for which types of people traits will be good versus poor predictors of their trait-relevant behaviors
Private self-consciousness
Self-monitoring
Criterion moderating variables
Specify the types of behaviors that traits will predict either well or poorly
Level of aggregation of the behavioral measure
Prototypicality of the behavioral criterion

10. Responses to Mischel’s criticisms
General traits do predict overall patterns of trait-relevant behavior fairly well. What they don’t predict well are single behaviors measured on a single occasion in a single situation.
Traits can be used to predict trait-relevant behavior in some, but not all, types of situations. In “weak” situations, traits are important in determining behavior. However, in “strong” situations, the influence of traits on behavior can be much more limited.
In general, an isolated trait accounts for about as much variance in a relevant behavior as an isolated situational variable does Richard, Bond, and Stokes-Zoota (2003). The typical correlation in each case is about .20.

11. Outcome of the debate
Mischel’s (1968) critique encouraged debate in personality psychology about the importance of traits compared to situational factors in causing behavior
Both sides tempered their views: Trait psychologists acknowledged the importance of situational factors, and situationists acknowledged the importance of traits
The debate led to two lasting changes: a focus on person-situation interaction and the importance of aggregation

12. Person X situation interaction
Personality and situation interact to produce behavior
Differences between people make a difference only under certain circumstances.
Situational specificity: Certain situations can provoke behavior that is out of character for an individual.

13. Aggregation
With regard to the predictor variable, longer tests are more reliable than shorter ones and are better measures of traits.
With regard to the outcome variable, a single behavior measured on just one occasion may be influenced by a variety of circumstantial features that are unrelated to personality.
Creating aggregated measures of behavior tends to “average out” the effects of these circumstantial features and allow the influence of the trait to emerge more clearly from the data.

14. Aggregation
Aggregation implies that traits are only one influence on behavior.
Aggregation also implies that traits refer to the person’s average level of the trait-relevant behavior as it is displayed over time.
At this point in time, it seems unlikely that personality psychologists will be good at predicting single acts that take place on single occasions.