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Interpersonal Expectancy Effects and Human Performance Research Honica J. Harris and Robert Rosenthal Humans have long tried to surmount their traditional limitations and to increase their performance. Long ago such efforts were aided by social institutions of religion, proto-meticine, and magic. More recently, such efforts have been aided by social institutions of science ant its associated technologies. Systematic programs have been developed with such aims as improving communication, accelerating learning, ant increasing conscious control over physiological processes. Because the promise of enhancing huma.. performance is so appealing, considerable resources, both in terms of time ant money, are being invested in these programs. The time has come to step back and evaluate human performance technologies so that resources may be directed more appropriately. The purpose of this paper is to aid in such an evaluation. We will focus specifically on the possible influence of interpersonal expectancy effects on several human performance technologies. The paper advances in three steps: First, we describe the methodological, theoretical, and empirical issues relevant to the study of expectancy effects, including how expectancy effects are mediated. Second, we describe each of several types of human performance research and speculate on the extent to which expectancy effects may be responsible for the experimental results. Finally, we discuss more generally how the literature on expectancy effects can be applied to the development~and evaluation of human performance technologies. Interpersonal Expectancy Effects Def ini~cion ~ . An interpersonal expectancy effect occurs when a person (A), acting in accordance with a set of expectations, treats another person (B) in such a
2 manner as to elicit behavior that tends to confirm the original expectations (Rosenthal, 1966, 1976~. For example, a teacher who believes thee certain pupils are especially bright may act more warmly toward them, teach them more material, and spend more time with them. Over time, such a process could result in greater gains in achievement for those students than would have occurred otherwise. The concept of an expectancy effect was first introduced by Merton (1948) in his discussion of the self-fulfilling prophecy, which he defined as "a false definition of the situation evoking a new behavior which makes the originally false conception come true" (p. 195). The first systematic application of the concepts of expectancy effects in the field of psychology came in the 1960s with a program of research on experimenter expectancy effects (e.g., Rosenthal, 1963). This research demonstrated that the experimenter's hypothesis may act as an unintended determinant of experimental results. In other words, experimenters may obtain the results they predicted not because the relationship exists as predicted in the real world but because the experimenters expected the subjects to behave as they did. Evidence for Interpersonal Expectancy Effects Although originally fraught with controversy, the existence of interpersonal expectancy effects is no longer in serious doubt. In 1978, Rosenthal and Rubin reported the results of a meta-analysis of 345 studies of expectancy effects. A meta-analysis is the quantitative combination of the results of a group of studies on a given topic. This meta-analysis showed that the probability that there is no relationship between experimenters' expectations and their subjects' subsequent behavior is less than .0000001. The practical importance of expectancy effects was also substantial; the mean
3 ef feet size of expectancy ef fects across the 345 studies was equivalent to a correlation coef f icient of . 33 . This meta-analysis also investigated the importance of expectancy ef fects within a wide variety of research domains. There were eight categories of expectancy studies: reaction time experiments, inkblot tests, animal learning, laboratory interviews, psychophysical judgments, learning and ability, person perception, and everyday situations or field studies. Although effect sizes Wearied across categories, the importance of expectancy effects within each category was firmly established. These results suggest that expectancy effects may occur in many different areas of behavioral research and emphasize the importance of taking into account the possibility of expectancy effects when des igR ing and conducting studies. Although initially focused on the psychological experiment as the domain of interest, research on expectancy effects turned quickly to other domains where expectancy effects might be operating, domains such as teacher-student, employer-employee, and therapist-client interactions. Over the years, research interest has also turned from merely documenting the existence of expectancy effects to delineating the processes underlying expectancy effects. Methodological Implications of ExDectancv Effects Experimenter expectancy effects are a source of rival hypotheses in accounting for experimental results. In other words, a given result could be caused not by the independent variable under investigation but rather by the experimenter's expectation that such a result would be obtained. As rival hypotheses, expectancy effects can be considered a threat to the internal validity of a study; they are a source of systematic bias rather than random error. Consequently, expectancy effects present a serious danger to the
4 interpretation of results: Increasing random noise merely makes it more difficult to obtain significant results, but increasing systematic bias can result in completely erroneous cone lus ions . Experimenter expectancy effects are a potential source of problems for any research area, but they may be especially influential in more recent research areas lacking well-established findings. This is because the first studies on a given treatment or technique are typically carried out by creators or proponents of the technique who tend to hold very positive expectations for the efficacy of the technique. It is not until later that the technique may be investigated by more impartial or skeptical researchers, who may be less prone to expectancy effects operating to favor the technique. Many of the human performance technologies of interest in the present paper are relatively recent innovations, and thus may be especially susceptible to expectancy effects. In principle, expectancy effects could be investigated by introducing expectations as a manipulation in addition to the independent variable of theoretical interest. This method, which will be described in detail later, allows the direct comparison of the magnitudes of the effects due to the phenomenon and effects due to expectancies. Another approach, perhaps even richer theoretical ly, is to examine directly the processes underlying expectancy effects as they occur in various areas. In some areas, such as the area of teacher expectancy effects, a considerable amount of research has been conducted in this manner, and there is now a good general understanding of what variables are important in mediating teacher expectancies. However, in other areas, such as the human technologies of interest here, this background research is lacking. The best that can be done in such cases is: (a) to
5 analyze the situations of interest, (b) to determine whether mediating mechanisms shown to be important in traditional research areas are likely to be present in the new areas, and (c) to estimate the extent to which expectancy effects court be influential in the new area. The present paper undertakes such an analysis. Mediation of Interpersonal Expectancy Effects Basic Issues A primary question of interest with respect to expectancy effects is the question of mediation: How are one person's expectations communicated to another person so as to create a self-fulfilling prophecy? This question in turn can be broken down into two components. The first component is the differential behaviors that are displayed by the expecter as a result of holding differential expectancies (the expecter-behavior link). For example, in what ways do teachers treat their high expectancy students differently? The second component is the differential behaviors that are associated with actual change in expectee behavior and self-concept (the behavior-outcome link). For example, what teacher behaviors result in better academic performance by the students? Both these aspects are critical in understanding expectancy mediation, for even if we could show an enormous effect of expectancy on expecter behavior (e.g., teachers smile more at high expectancy students), that behavior would not be important in expectancy mediation unless it actually impacted on the expectee to create better outcomes (e.g., being smiled at leads to better grades). The Four-Factor "Theory" Rosenthal (1973a, 1973b) proposed a four-factor "theory" of the mediation of teacher expectancy effects. In this view, four broad groupings of teacher