The Wall Street Journal recently served readers this slap-in-the-face headline: “You’re Not as Smart as You Think”. The piece was written by two psychologists, Christopher Chabris and Patrick Heck, detailing a new study they and another colleague published in PLOS One, in which they found that 65 per cent of Americans reported they were “more intelligent than the average person”.

The survey respondents actually seem pretty modest, in contrast to past claims such as “everyone thinks they are above average”. In the Journal contributors’ study, 23 per cent of people disagreed with the statement that they were above average, and 12 per cent said they did not know. Of the 65 per cent who believed themselves to be above average, a good number probably are.

So some people aren’t as smart as they think they are, and the headline applies to them. But others are smarter than they think they are. More on that later.

Using the word “average” in the question introduces an additional layer of confusion. Half of everyone must be below the median; that is the definition of median. But another type of average, the mathematical mean, can differ from the median when there is a lopsided distribution.

Accusing people of overconfidence also assumes that intelligence is well-defined and quantifiable enough that there is real meaning in comparing ourselves with an average.

Chabris, who works for Geisinger Health System in Pennsylvania and has a background in both psychology and neuroscience, said he set up the study not to knock people off self-constructed pedestals, but to investigate the present level of belief in various brain myths. Two that particularly irk him: the notion that people are either right or left-brained, and the myth that most of us only use 10 per cent of our brains.

Belief in the 10 per cent myth is so pervasive that even some people who are genuinely above average buy into it. It may have originated as a distortion of the idea that many people do not live up to their potential. Experts say there is ample evidence that even the most blatant underachievers are using most of what is in their heads.

Chabris said he and his colleagues surveyed a cross-section of 2,821 Americans, by phone or online, about their level of beliefs in a selection of popular myths. They also included a question about how the subjects felt about their own relative intelligence as a way to test what Chabris called a cliché of popular psychology — the notion that most people think they are above average in intelligence.

So the study was designed both to probe belief in disproved myths and to test whether another widely held belief was in fact false. The result was that Americans, at least, are not as impressively overconfident as the cliché would suggest. Women were considerably less confident than men, people older than 44 less confident than younger people. College graduates are slightly under-confident. So if you are female, over 44, and have a degree, take heart: there’s a good chance you are smarter than you think.

How, I asked, were people supposed to decide if they were above or below average? IQ scores? SATs? School report cards? IQ is at least quantifiable, but scientists disagree on how well it reflects what most people think of as intelligence.

Most people don’t know their IQ anyway, Chabris said, nor do most remember their SAT scores. He and the other researchers cast no negative judgment on the test subjects who over or underrate themselves. While overconfidence can lead to arrogance, he and Heck wrote, “expressing confidence also can bestow benefits, even if that confidence is sometimes undeserved. Confident people are seen as being more competent and higher in social status than humble people”.

If this is true, then it implies that society would tend to undervalue older, educated women, relative to younger people and males. While overconfidence might be more common, under-confidence might, ultimately, cause more harm.

I looked into a different flavour of overconfidence for a column published last year, which discussed America’s self-described genius of a president, as well as columnist George Will’s contention that Donald Trump’s overconfidence is a disorder.

The psychologists I interviewed brought up something called the Dunning-Kruger effect, more a brand of human folly than a disorder, in which people who lack a skill tend towards overconfidence because they have no idea what it takes to possess that skill. It is part of learning a skill to recognise how far you need to go to reach a desired level, and where to shore up weaknesses.

Intelligence is problematic because psychologists are still debating whether it is more like an acquired skill, which we can bolster, or a static trait. You cannot, unfortunately, just tap into the mythical, unused 90 per cent of your brain. So maybe, when in doubt, it is smart to assume you are smart. And for those whose jobs involve making judgments about other people, remember that the most competent are not necessarily the most confident.

• Faye Flam is a Bloomberg Opinion columnist. She has written for The Economist, The New York Times, The Washington Post, Psychology Today, Science and other publications. She has a degree in geophysics from the California Institute of Technology