This is a very intelligent question. It is probably good to start with a definition of these terms.
- A stereotype is the popular belief about someone, group, or thing with little basis in reality. It is to make gross generalizations.
- A halo effect is when one good quality of a person is used to make good generalizations about that person with no basis.
- Projection is when a person takes usually unwanted feelings or ideas and ascribes them onto others, when they are really from that person.
An example of stereotyping is when someone ignorantly says that all women cannot drive. This is completely false, not to mention chauvinistic and foolish.
An example of a halo effect is when we think that a celebrity whom we like, such as Tom Cruise, and assume that he is intelligent, kind, compassionate, and caring. He might be these things, but we cannot automatically assume them, just because we like his acting.
An example of projection is when a person says that she does not like me, when in fact that person is the one that does not like that other person.
The halo effect comes into play when we take one attribute of a person and we use it to form our overall impression of the person. We often do this with people with whom we are infatuated. If you think someone is really good-looking, you might also come to believe that they are witty and kind even if they really are not. The halo effect makes you take one good attribute (looks) and believe that it means that they are good in other ways as well. This can, of course, work negatively as well. You can take a bad attribute and believe that it indicates that the person is completely bad.
Stereotyping occurs when we judge all people of a certain group by preconceptions that we have about their group. This happens a great deal in high school. We stereotype all “jocks” as stupid and rowdy. We stereotype cheerleaders as airheaded and/or stuck up. Any time that we think that all members of a group are some way just because they are members of that group, we are stereotyping.
Projection occurs when we take feelings of our own that we do not like and we attribute them to other people. This is a common defense mechanism. A common example of this would be if we were tempted to cheat on a test (or if we actually did). We would say that everyone else in the class wanted to cheat or that they really were cheating. We would say this not because it was true but because we do not want to admit our own desire to cheat.