Book Definition: A faulty heuristic caused based on the presumption that once people or events are categorized, they share all the features of others members in that category.

In Your Own Words

  • Stereotyping or "pigeonholing" someone or something; unintentional prejudice.
  • Assuming that because someone or something shares one characteristic with a group of people/things, they share all of the characteristics of that group.
  • Think because one person has the same quality with another group, that the person is just like all the rest of that group.


  • Believing that all blondes are dumb
  • From Mr. Wray's song: "I'm biased because I put you in a category in which you may or may not belong. Representativeness bias: don't stereotype this song."
  • Looking at someone who is wearing glasses and is dressed business-like or formally, then concluding that they are intelligent.
  • Assuming that people who wear sandals, ride a bikes everywhere, and support liberal causes are vegetarians because they hold enough of the characteristics of your concept of a "vegetarian" to belong to that group.
  • If you are Irish, people often stereotype you as a heavy drinker, even though they have no evidence of this and you have never even considered consuming alcohol in your life.
  • Due to multiple recent television programs, a representative bias has formed that people from New Jersey are unintelligent and only enjoy partying, making money, and being too tan.
  • Seeing someone hang out with a certain group of people and you immediately think they do what that group does.
  • Seeing someone doing their homework during lunch instead of eating with their friends and you think they don't have any friends.
  • Because someone is wearing sweatpants once, you assume that they are lazy or don't put effort into what they wear.
  • Judging a book by its cover.
  • In the movie Legally Blonde she goes to Harvard and people there don't think she is smart because of her bubbly personality.
  • Believing that all Asians are smart and good at math.

Additional Resources

  1. Mr. Wray's Cognitive Bias VideoSong: