How Social Categorization Affects People Negatively


By Catherine A. SandersonAmherst College

Stereotypes are a type of mental shortcut that help us simplify a complex world. According to social categorization theory, which was developed in the 1970s, we quickly divide people into groups on the basis of common attributes, namely into in-groups, people like us versus out-groups, people who are not like us. This differentiation can be done on virtually any grounds.

A scence from of an NBA basketball match
There is weak evidence that supports officials’ decisions in professional sports leagues such as the NBA being affected by biases. (Image: Tom Hagerty/Public domain)

Social Categorization 

Although dividing people into groups is not inherently problematic, it can lead to two biases. First, there’s a tendency to assume that members of the out-group are all pretty similar to one another, which is known as the out-group homogeneity effect. 

So, once we’ve divided people into groups, we see people in our in-groups as representing a full range of characteristics, but people in our out-groups as basically all the same. This makes it far easier to use stereotypes and just to see everyone in a particular out-group as the same—people from Texas, or women in sororities, or Ivy League professors. It’s particularly easy to make this assumption when you don’t have a lot of contact with people in the out-group.


The second bias resulting from dividing people into in-groups and out-groups is we show in-group favoritism, meaning a tendency to see people who are like us in a more favorable light—as smarter, nicer, more deserving of resources, and so on. We also discriminate in favor of people in our in-group.

Research examining calls made by officials in professional sports leagues shows some weak evidence of in-group favoritism by race. NBA players have fewer fouls called against them and score more points when their own race matches that of the referees. White umpires provide a larger strike zone to white pitches and a smaller strike zone to white batters.

Stereotypes Can Be Dangerous

A group of men watching sports
Social categorization might be linked to why watching sports with friends rooting for the other team is so frustrating. (Image: Adriaticfoto/Shutterstock)

Now, these are all relatively small effects at most, and some research on officiating has disputed the role of bias, but such studies remind us, in any case, to be alert to the possibility that even people tasked with remaining neutral may lapse into favoring members of their in-group.

Once we’ve formed stereotypes about members of a particular group, stereotypes do tend to be maintained, in part because we thereafter perceive people in that group in line with these beliefs, a phenomenon psychologists describe as perceptual confirmation. 

People see a baby’s reaction to a jack in the box as angry if they believe that baby is a boy versus sad if they believe the baby is a girl. Officials see a football player’s touchdown celebration differently if that player is Black than if that player is white. This tendency to see things in different ways depending on our group membership explains why it can be so frustrating to watch a game with someone who is rooting for the other team.

This article comes directly from content in the video series Introduction to PsychologyWatch it now, on Wondrium.

The Aerobics Teacher Who Was Smart

The power of perceptual confirmation was brought home to me vividly a number of years ago, when I had a part-time job teaching aerobics at a local health club. At the time, I was a graduate student at Princeton University; I had received my masters and was working on my doctorate. Yet when people interacted with me at the gym, they clearly assumed I was pretty dumb; that’s a stereotype some people have of aerobics instructors. 

Young people in an aerobics class
Social categorization can make it hard for some people to believe that an aerobics teacher has a master’s degree. (Image: Fizkes/Shutterstock)

At some point, I mentioned to my class that I was cutting back my hours at the gym to concentrate on school. And people in my class were overwhelmingly supportive, telling me that “education was so important” and clearly implying they assumed I was finishing up my GED for high school. 

Of course, in reality, I was reducing hours because I needed to devote more time to finishing my dissertation, but that wasn’t the image that was coming to mind when those folks at the gym thought about an aerobics instructor focusing more on school.

The Self-fulfilling Prophecy

So, it’s not just that we see things in line with our expectations. Once we’ve formed a stereotype, we also treat that person in line with our beliefs, which in turn elicits behavior that confirms these biases. This process is known as self-fulfilling prophecy, an expression coined by sociologist Robert Merton in the late 1940s.

One of the earliest studies to demonstrate this effect in a dramatic way was conducted at an elementary school in San Francisco in 1964. A Harvard psychologist named Robert Rosenthal told teachers in a San Francisco elementary school that the results of an IQ test had revealed that a few of their students were “late bloomers,” meaning that they would experience a substantial increase in intelligence during the upcoming year. 

He told them that the principal believed it was important for them to receive this information, so he specifically identified which of these students were in fact expected to show this increase. In reality, these kids were chosen at random. But at the end of the school year, these kids in fact did show a dramatic boost in IQ—especially for the youngest children—those in first grade, who averaged 15 points gains over those not in the experimental group.

Although we don’t know precisely how teachers may have changed their behavior, this study illustrated that expectations can dramatically alter reality. Similarly, stereotypes we hold about our own identity can also affect our own performance. In an example of what is called stereotype threat, students taking standardized tests do worse if reminded of an identity they hold that is stereotyped as doing poorly in a particular domain.

Common Questions about How Social Categorization Affects People Negatively

Q: What is the out-group homogeneity effect?

When social categorization happens, people tend to assume that those in the out-group have the same characteristics. This makes it easier to write off everybody in the out-group as the same and create stereotypes; it’s called the out-group homogeneity effect.

Q: What are the two main problems of social categorization?

The first problem of social categorization is the out-group homogeneity effect that people tend to oversimplify the characters of the out-group. The second problem is in-group favoritism which there exists considerable evidence for.

Q: What is a self-fulfilling prophecy?

A self-fulfilling prophecy is a process that occurs after we form stereotypes for ourselves. Our stereotypes create biases that elicit behavior which in turn confirms the biases. This cyclic process is called a self-fulfilling prophecy, one of the negative consequences of social categorization.

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