Rosenthal effect

n. The Rosenthal effect, named after the psychologist Robert Rosenthal and sometimes referred to as the Pygmalion effect, is the powerful influence of expectancies on human behavior. Rosenthal's research was originally conducted in educational settings in the 1960s, and the findings suggested powerful effects of teacher expectancies on student progress. The researchers randomly selected some students and (falsely) informed teachers that those students, who had ostensibly performed in the top 20% on a measure of intelligence, were “bloomers,” who were likely to progress at an advanced rate. When researchers gathered intelligence data at a later point in time, those who had been identified as “bloomers” showed more improvements than those who had not.

Social psychologists have extensively studied the effects that expectations can have on the behavior of others in our social environments, an area of research known as self- fulfilling prophecy. Data from a variety of areas point to the powerful influence of expectancies, effects which are manifest in sometimes subtle 
verbal and nonverbal behavior toward others. Research has also shown that expectancies can influence others without our knowledge and that efforts to minimize or eliminate expectancy effects are met with limited success. In other words, even if we are aware that our expectancies have the potential to influence 
others, our efforts to prevent these effects are met with limited success. The double-blind procedure, in which both experimenters and participants are unaware of the researchers' objectives, is an effective and common way for researchers to avoid expectancy effects in their research. – MWP

▶ See also DEMAND CHARACTERISTICS