What Is the Halo Effect?

Post Author: Bill Pratt 

It has nothing to do with the popular video game, but like confirmation bias, it is a concept you need to understand because it impacts all of us, and we are mostly unaware.

Psychologist Daniel Kahneman, in his book Thinking, Fast and Slow, describes the halo effect.

If you like the president’s politics, you probably like his voice and his appearance as well. The tendency to like (or dislike) everything about a person— including things you have not observed— is known as the halo effect. The term has been in use in psychology for a century, but it has not come into wide use in everyday language. This is a pity, because the halo effect is a good name for a common bias that plays a large role in shaping our view of people and situations. It is one of the ways the representation of the world that System 1 generates is simpler and more coherent than the real thing.

Kahneman provides a concrete example:

You meet a woman named Joan at a party and find her personable and easy to talk to. Now her name comes up as someone who could be asked to contribute to a charity. What do you know about Joan’s generosity? The correct answer is that you know virtually nothing, because there is little reason to believe that people who are agreeable in social situations are also generous contributors to charities.

But you like Joan and you will retrieve the feeling of liking her when you think of her. You also like generosity and generous people. By association, you are now predisposed to believe that Joan is generous. And now that you believe she is generous, you probably like Joan even better than you did earlier, because you have added generosity to her pleasant attributes.

Real evidence of generosity is missing in the story of Joan, and the gap is filled by a guess that fits one’s emotional response to her. In other situations, evidence accumulates gradually and the interpretation is shaped by the emotion attached to the first impression.

Impressions of a person are gained over a period of time, but the halo effect causes us to overweight first impressions over later impressions. Here is the problem stated:

The sequence in which we observe characteristics of a person is often determined by chance. Sequence matters, however, because the halo effect increases the weight of first impressions, sometimes to the point that subsequent information is mostly wasted.

Early in my career as a professor, I graded students’ essay exams in the conventional way. I would pick up one test booklet at a time and read all that student’s essays in immediate succession, grading them as I went. I would then compute the total and go on to the next student. I eventually noticed that my evaluations of the essays in each booklet were strikingly homogeneous. I began to suspect that my grading exhibited a halo effect , and that the first question I scored had a disproportionate effect on the overall grade.

The mechanism was simple: if I had given a high score to the first essay , I gave the student the benefit of the doubt whenever I encountered a vague or ambiguous statement later on. This seemed reasonable. Surely a student who had done so well on the first essay would not make a foolish mistake in the second one! But there was a serious problem with my way of doing things. If a student had written two essays, one strong and one weak, I would end up with different final grades depending on which essay I read first. I had told the students that the two essays had equal weight, but that was not true: the first one had a much greater impact on the final grade than the second.

In the next post, we will look at some implications of the halo effect.