Are blondes dumber than brunettes? No, of course not – but generally, people think they are. Similarly, you probably don’t want a more experienced doctor in the ER, and there’s a pretty good chance any given teenager is less horny than you right now.

So why is it that we tend to assume the opposite in all these cases? It’s all due to a cognitive bias known as the “halo effect” – the tendency to take a single factor about a person and use it to draw sometimes wildly unrelated conclusions about their character.

What is the halo effect?

You know how, in medieval art, all the angels were drawn as beautiful and resplendent, surrounded by a golden halo, to convey just how good and blessed they were? The halo effect is basically that, but in reverse.

“It is the idea that global evaluations about a person (e.g. she is likable) bleed over into judgements about their specific traits (e.g. she is intelligent),” wrote Jeremy Dean, psychologist and author of the website PsyBlog.

“It is sometimes called the ‘what is beautiful is good’ principle, or the ‘physical attractiveness stereotype’,” he explained.

The halo effect, basically, is why you’re convinced your favorite celebrity must be a cool guy to hang out with. It’s why your teachers tell you to write neatly in exams, and why designer jeans cost so much more than generic brand. It’s even the reason it’s so shocking that Adolf Hitler loved dogs and children.

For the classic example, it’s easiest to go back to the paper that first coined the "halo effect" more than 100 years ago. Considering surveys conducted in places like the army, or factories, asking people to rate their comrades on qualities like skill, intelligence, reliability, and even things like their physique and bearing, psychologist Edward Thorndike noticed something suspicious about the answers: they were too neat.

“The estimates of the same man in a number of different traits such as intelligence, industry, technical skill, reliability, etc., etc., were very highly correlated and very evenly correlated,” Thorndike reported. “It consequently appeared probable that those giving the ratings were unable to analyze out these different aspects of the person's nature and achievement and rate each in independence of the others.”

In other words, if the workers thought their colleague was a good guy, they rated him higher than he objectively deserved for pretty much everything. If they didn’t like him for some reason, the opposite was true.

“[I am] convinced that even a very capable foreman, employer, teacher, or department head is unable to treat an individual as a compound of separate qualities… in independence of the others,” Thorndike concluded. “The magnitude of the constant error of the halo, as we have called it… seems surprisingly large.”

Taken in by the halo

“Sure,” you may be thinking, “I can see how some people might fall for that – but not me. I’m too smart for that.”

That’s certainly what a group of students thought when they were recruited as test subjects back in 1977. In the now-classic experiment, social psychologists Richard Nisbett and Timothy Wilson told the volunteers that they were investigating whether the amount of exposure students had to a lecturer would influence how highly they rated them in an evaluation.

In fact, they were measuring something else: whether the lecturer’s likeability would influence their ratings. The students were split into two groups – one watched a video of a lecturer answering questions in a warm, friendly, and enthusiastic manner; the other watched a video of the exact same lecturer answering the exact same questions, but with a much worse attitude.

“Consistent with the halo effect, students who saw the ‘warm’ incarnation of the lecturer rated him more attractive, his mannerisms more likable and even is accent as more appealing,” explained Dean. 

And even after it was pointed out to them (twice!) that their judgments may have been affected by his likeability, they insisted that they had marked the lecturer objectively.

“[The] students had no clue whatsoever why they gave one lecturer higher ratings, even after they were given every chance,” Dean wrote. “They were convinced they had made their judgment about the lecturer’s physical appearance, mannerisms and accent without considering how likable he was.”

Why do we fall for it?

Humans are, let’s face it, little more than apes with a god complex – and as powerful and smart as we think we are, our brains really love taking the easy way out.

“The Halo effect… serves to increase the consistency of our evaluations and build easier narratives,” explained Eva Krockow, a researcher in decision-making at the University of Leicester, in an article for Psychology Today.

“People tend to avoid states of internal inconsistency,” she wrote. “It’s easier to build a mental image of a person that’s all positive than it is to carefully construct a nuanced picture, which involves both good and bad aspects, depending on the context.”

That can be a problem, since those ape brains of ours can also be hella superficial. The halo effect is most pronounced with regards to physical appearance, so if you’re short or ugly, prepare to be paid less and thought of as less intelligent and capable than your tall, attractive peers. Equally, beware the dating pool: the halo effect can make an attractive suitor’s racist jokes and possessive behavior seem less red than the massive crimson flags they are.

So how do we beat it? The only thing we can do, really, is to try to consciously maintain objectivity. “Biases are most influential when we allow for automatic, intuitive and emotional thinking to influence our judgements,” Krockow wrote. “To reduce the influence of cognitive biases, we therefore have to slow things down and control subjective feelings.”

By staying aware of the halo effect, stopping to consider whether it’s affecting our judgments, and – particularly in situations such as interviews or dates – creating and sticking to a predetermined list of “must-haves” and “must-not-haves”, regardless of how you feel about the candidate, we can all get a better handle on this omnipresent cognitive bias.

And let’s hope we do, to be honest. After all, who wants to lose a potential job, or friend, or even a partner, based solely on a bad haircut or a stray zit?

All “explainer” articles are confirmed by fact checkers to be correct at time of publishing. Text, images, and links may be edited, removed, or added to at a later date to keep information current.