Expectancy Effect

Expectancy Effect Definition

An expectancy effect occurs when an incorrect belief held by one person, the perceiver, about another person, the target, leads the perceiver to act in such a manner as to elicit the expected behavior from the target. For example, if Mary is told that a new coworker, John, was unfriendly, she may act in a more reserved manner around him, refrain from initiating conversations with him, and not include him in activities. John might then respond to Mary’s standoffish behavior by similarly not initiating conversations or activities with her, thus confirming her expectancy that he is unfriendly. Expectancy effects are thus a subcategory of self-fulfilling prophecies that occur in an interpersonal context.

Expectancy Effect Background

Expectancy EffectSelf-fulfilling prophecies have long been noted and studied by social scientists. The bank failures of the Great Depression are frequently offered as a classic example: An inaccurate rumor would circulate that a bank was about to fail. This would cause a run on the bank, with customers hurrying to withdraw their funds before the bank ran out of money. Banks, of course, do not keep enough cash on hand to cover all their deposits, so a run on the bank would eventually force it into failure, a victim of its clients’ false expectancies.

Research on expectancy effects began with the work of Robert Rosenthal, who looked at experimenters’ expectations. Rosenthal demonstrated that sometimes experimenters may obtain their results in part because their expectations led them to treat their experimental participants in a biased manner, eliciting the hypothesized behavior. This work led to the ultimate realization that researchers need to design their studies so as to prevent experimenter expectancy effects. Fortunately, there is an easy solution to this problem: If studies are run in which experimenters are blind to the experimental condition of the participants (i.e., if they do not know which participants are in the experimental vs. control groups), then it is impossible for them to bias their participants’ responses. The double-blind experimental design remains today the gold standard of research.

Research on expectancy effects then turned to other interpersonal contexts. The classic Pygmalion in the Classroom study showed that students whose teachers were told were academic bloomers (but who had in fact merely been randomly labeled as such) showed significant gains in IQ over the school year compared to students who had not been labeled academic bloomers.

Current Research on Expectancy Effect

Current research on expectancy effects has moved beyond mere demonstrations that they occur to identifying and understanding the theoretical and methodological variables that moderate expectancy effects.

In other words, for what kinds of people and in what kinds of situations are expectancy effects more likely to occur?

Research examining these questions indicates that, while there are individual differences that moderate expectancy effects, such as self-esteem, gender, and cognitive rigidity, situational factors such as the relative power of the perceiver and target and how long they have known each other appear to be more important predictors of expectancy effects. An expectancy effect is more likely to occur when the perceiver is in a position of greater power than the target (such as in a teacher-student relationship) and when the perceiver and target have not been previously acquainted. The longer the individuals know each other, the less likely it is that perceivers will either form or be influenced by incorrect expectancies.

Relatedly, much of the recent research in this area has been dedicated to the question of determining how powerful expectancy effects are in naturally occurring contexts as opposed to the laboratory. Laboratory experiments typically yield expectancy effects of larger magnitude. In the real world, accuracy effects (i.e., when the expectations formed by the perceiver reflect the actual abilities or traits of the target) appear to be more prevalent than expectancy effects, which occur less often or tend to be lower in magnitude.

Another major question in this area concerns the mediation of expectancy effects; in other words, what are the behaviors by which the perceivers’ expectations are communicated to the target? While the specific mediating behaviors involved depend on the context of the interaction, the vast majority can be classified as falling into the dimensions of affect or effort. Affect refers to the socioemotional climate that is created by the perceiver, and it involves primarily nonverbal cues associated with warmth and friendliness. Thus, a teacher who has high expectations for a student will smile more, use a friendlier tone of voice, and engage in more eye contact with the student. Effort refers primarily to the frequency and intensity of interactions between the perceiver and target. A teacher with positive expectations of a student, for example, will attempt to teach more material and more difficult material to that student, ask more questions, and spend more time talking with the student.

Expectancy Effects Importance

Because inaccurate expectations can have such serious ramifications, this remains a topic of social psychological research with considerable importance in both methodological and real-world domains. For example, knowing that experimenters’ expectations can unintentionally bias their results has led to major improvements in how researchers design and conduct experiments, in psychology as well as other fields such as medicine.

Of greater social importance is understanding the role that others’ expectations of a person can play in determining a person’s outcomes in life, ranging from events as trivial as whether he or she gets along with a new coworker to matters of tremendous significance, such as whether he or she ultimately succeeds or fails in school. To say that expectations can have self-fulfilling consequences is therefore a message both of warning and hope. It is a message of warning because inaccurate negative expectations can doom an otherwise-capable person from achieving his or her full potential. It is also a message of hope, because positive expectations on the part of an important person in one’s life—parent, teacher, employer—can help lead one to accomplishments only dreamed of earlier.


  • Rosenthal, R. (1994). Interpersonal expectancy effects: A 30-year perspective. Current Directions in Psychological Science, 3, 176-179.