What is the halo effect and why does it matter?

University of Warwick Professor Daniel Read explains the halo effect and how it skews our judgment—whether we’re evaluating people, essays, or companies.

You’ve surely heard the adage, “Don’t judge a book by its cover.” But let’s be honest: you’ve probably done it anyway. Maybe you picked up a novel because the artwork caught your attention—or passed on one because its cover was lackluster. It’s unlikely this led to disaster (though you may have missed out on a great read).

But of course, the saying is less about actual books and more of a warning against the instinct to let superficial features like appearance guide important decisions where those features are irrelevant. It’s a tip not to hire someone because you like the way they look, which may unwittingly lead you to assume you’ll also like their work. And it’s an admonishment for the stock you might not buy because its name sounds silly (so you assume it couldn’t turn a profit).

This tendency to let one standout trait—like attractiveness or a catchy name—shape our broader judgment is what behavioral scientists call the halo effect. It’s a bias that can quietly influence choices in domains ranging from hiring and dating to shopping and investing.

This month’s Q&A dives into the halo effect with University of Warwick Professor and behavioral scientist Daniel Read. Read explains what the halo effect is, why we fall for it, and how we can make better choices once we understand it. I hope his advice leaves you thinking twice the next time you're tempted to judge a book—or anything else—by its cover.

But first, here are a few listens and reads I’ve enjoyed recently that I think you might like too.

This Month’s Recommended Listens and Reads

• Little Bits of Happiness: Our spring 2025 season finale of the Choiceology podcast focuses on how your happiness is affected by the separation between life’s highs and lows, featuring an interview with UC Berkeley Professor Ellen Evers.

• The Attack on Harvard is Deranged: Harvard Professor Stephen Pinker’s balanced piece will help you see why defending valuable but imperfect research institutions like Harvard is well warranted.

• Unforgiving Places: University of Chicago Professor Jens Ludwig’s important new book on the origins of American gun violence received a rave review from Malcolm Gladwell in the New Yorker earlier this month, and I also highly recommend it.

Q&A: What is the halo effect and why does it matter?

In this Q&A from Choiceology, University of Warwick Professor and behavioral scientist Daniel Read explains the halo effect and how it skews our judgment—whether we’re evaluating people, essays, or companies.

Me: Let’s start with a description of the halo effect. What is it exactly?

Daniel: The halo effect says that when we make multiple judgments about any person or object’s quality—like whether they're good or bad—those judgments tend to be more highly correlated than is warranted.

One of the areas where it has been studied the most is in judging people based on physical attractiveness. It turns out that if people are perceived as physically attractive, then their personality is judged as being nicer, they tend to be assumed to be more successful and so on. But it's been looked at in a lot of other contexts as well. For example, when people mark student essays, if they mark, say, two in a row by the same student, and they see the first essay is good, they're likely to be quite charitable towards the second essay. Even if the second essay is not a great essay. But if it's ambiguous, they'll be quite generous toward it. Similarly, if the first essay is not good, they won't be as generous towards the second essay.

Me: Could you describe some early research on the halo effect?

Daniel: The very first study of the halo effect was from 1920 by Edward Thorndike. He looked at many, many different ratings of soldiers on a number of dimensions. What Thorndike observed was that the correlations between all of the ratings were much, much higher than they should have been, and even correlations between things that probably shouldn't have been correlated at all were actually quite high. For example, intelligence and strength. These were soldiers. Intelligence and strength, which probably are not correlated particularly strongly, in fact, perhaps not at all, were correlated at 0.7 in these ratings.

Me: Which is really high, right? Because correlations range from zero to one, and 0.7 is…that's about as much correlation as you ever see between traits in the natural world.

Daniel: Exactly, yes. He said that the correlations were three or more times as high as they should have been. There is another classic study on essays that's pretty interesting. They had male raters look at essays, and the essays were rated in advance as either good or poor. The male raters were also given a picture of the person who had written each essay and who was either attractive or unattractive. What they found is that the poor essays were rated much more highly if the writer was attractive. And also, the ability of the writer was judged as being much greater if they were attractive than unattractive.

There’s another study I find kind of cute in which a person came to a classroom, and they gave a little discussion, and then they left the room, and the teacher asked everyone, "Well, how tall was the person?" Now this person was either described as being a postdoc or an assistant professor or a full professor, and what they found is that the estimated height of this person went up with the person's status, where the full professor was judged as taller than the postdoc and the postdoc less tall than the assistant professor and so on.

Me: Incredible. Can you explain what we know about why the halo effect arises?

Daniel: I think the main cause is that most of the time when we’re making judgments about two traits of a person or thing, they tend to be a bit correlated, and we know that they're related in some way. This is a conscious effect: we know that, say, attractiveness might indeed be correlated with personality on average because an attractive person may have different experiences and so forth. But how big is that correlation? Well, it's probably pretty small in reality. Most correlations in the world are pretty small. But how do you, in your judgments, express a small correlation? It's quite hard to do.

I don't think that it's necessarily that the halo effect is always wrong, but the halo effect itself is an extreme response when we should be giving perhaps a moderate response in most cases.

Me: That makes a lot of sense. I know you've done some really interesting recent research on the halo effect in the domain of corporate social responsibility, or CSR. Could you talk a little bit about that work?

Daniel: Yes. This work was done with Sofía López-Rodríguez and Craig Smith. We did a series of studies where we described companies to our respondents—either a company which had undertaken some kind of positive CSR initiative or had not. An example would be a company which had an ambitious recycling program for printer cartridges. Then we asked whether people assumed this company had done other things, and we asked both about specific actions and more general things like: “Does it do things that are good for the environment?”, “Does it do things that are good for its customers?”, and so forth.

First, we found that the company that was recycling printer cartridges would be evaluated very positively for all types of other environmental activities, but in addition, there was a generalization to other domains of activity. It was expected that the company would also treat its customers better. It would also do more for the community, and so forth. We got a halo effect within the domain, but in addition, it was cross domain. It shows that one action for a company can have quite an impact on how people judge it.

And those inferences are perhaps not fully warranted. The company is probably not doing all these things. There's no real reason to assume it has, yet, nonetheless, we make these positive judgements.

Me: I have to say, as a woman, it makes me think a lot about makeup and all the attention that's paid to physical attractiveness in our culture, and it makes me sad because it seems to suggest that those kinds of investments are wise as opposed to unnecessary.

Daniel: Yes, I'm afraid that does seem to be what it suggests.

Me: I guess there’s also a positive spin, which is to recognize that when you do things that are genuinely good, you really put in effort and score well on a test or give a great presentation or put together a fabulous podcast, that not only will you incur benefits in terms of how you're assessed on that activity, but you'll actually get spillover benefits. So all good actions may do us even more good than we appreciate objectively. Maybe that's a nicer way to think about it.

Daniel: That's absolutely right. We can think that whatever we do, we're creating an impression on people, and that impression is going to be generalized, so you want to make a good impression.

Me: Do you have any advice for how people can improve their everyday decisions now that they better understand the halo effect?

Daniel: Well, you can approach decisions differently. If you have to make multiple assessments, let's say you need to evaluate an employee, and you have to evaluate the employee on several different dimensions, either don’t make all the evaluations at once, or try to find objective criteria by which to make the evaluations, or you can even have different people make evaluations of different dimensions.

Me: That’s excellent advice. As many independent judgments as possible and as much objectivity as possible to protect against bias from the halo effect. Thank you.

This interview has been edited for clarity and length.

To learn more about Daniel’s work, listen to the episode of Choiceology where we dig into the halo effect.

That’s all for this month’s newsletter. See you in July!

Katy Milkman, PhD

Professor at Wharton, Host of Choiceology, an original podcast from Charles Schwab, and International Bestselling Author of How to Change

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