Myers-Briggs Was Built by a Mystery Novelist and Her Mother. Neither Had Studied Psychology. 88% of the Fortune 500 Have Used It.

ISSUE #049 · MYTHS & MISINFORMATION · AUGUST 2026

There are sixteen of them. You have almost certainly been assigned one. Maybe at an away day, maybe by a recruiter, maybe at two in the morning on a free website that promised to explain why your last relationship ended.

Four letters. INTJ. ESFP. A paragraph describing you as a rare visionary, or a warm pragmatist, or a quietly indispensable organiser. It lands. That is the whole trick, and we will come back to why it lands.

The Myers-Briggs Type Indicator is the most widely administered personality assessment on Earth. Its publisher says 88 per cent of Fortune 500 companies have used it, that it operates in 115 countries, and that it comes in 29 languages. Roughly two million people take some version of it every year.

It was not built by psychologists. It was built by a woman who wrote detective fiction and her mother, who had a degree in agriculture, working from their homes, largely during the Second World War, with no training in psychology, psychometrics or statistics between them.

That is not an insult. It is the documented record, and both women were open about it. The interesting question is not how two amateurs invented it. It is how the thing survived eighty years of professional psychology telling anyone who would listen that it does not work.

In 1915, Isabel Briggs brought her fiancé home. His name was Clarence Myers, known as Chief, and he was studying law.

Isabel’s mother, Katharine Cook Briggs, could not place him. He was decisive and outward-facing where the Briggs family were reflective and inward. Katharine — a writer with a college degree in agriculture, who had been home-schooled by her own father until she left for college at fourteen — decided to work out why.

She began cataloguing the people around her, building a homemade system she called the Four Types. Part of the motive was maternal: if she could understand Chief rather than reject him, she would not lose her daughter.

Then in 1923, Carl Jung’s Psychological Types appeared in English translation. Katharine read it and recognised something more developed than her own scheme. She became a committed Jungian, corresponded with Jung, and wrote about his typology for popular magazines.

That is the founding document of the world’s dominant personality test: a mother’s attempt to understand the man her daughter was marrying, grafted onto a Swiss psychiatrist’s untested theory.

Isabel Briggs Myers took the project further than her mother ever did. Her degree from Swarthmore was in political science. Her professional success to that point had been a prize-winning mystery novel.

From 1942 she built an actual questionnaire — 172 forced-choice items, each asking the respondent to pick A or B. She tested it on her son’s high-school class, on students at nearby colleges, on the military units of family friends. Her father, a physicist who directed the Bureau of Standards, used his academic contacts to get the questionnaire administered to incoming medical students at George Washington University, which she parlayed into several thousand more.

She insisted it never be called a test, because there was no pass or fail. It was an Indicator.

The first booklets went on sale in 1943 at fifty cents each. She had presented the instrument to Edward N. Hay and Associates, a firm specialising in white-collar workplace aptitude testing. The first order came from the Office of Strategic Services in Washington.

This matters, because of how the test is sold today. It is now marketed as self-discovery — a route to knowing yourself. It was designed as an instrument of corporate and wartime efficiency: a way of sorting people into the jobs the war economy needed filled. In 1957 Myers sold it to a psychometric publisher, and the sorting became a business.

The MBTI rests on Jung’s 1921 typology. So it is worth asking what Jung thought about sorting people into categories.

He was blunt about it. Asked directly whether he saw the world as divided into introverts and extroverts, he said there is no such thing as a pure introvert or extrovert — and added that such a person would belong in an asylum. Elsewhere he wrote that classifying individuals by type meant nothing at all, and that classification had never much interested him. He described his own scheme as an orientation, a rough set of reference points, useful mainly for explaining a husband to a wife.

He also wrote that no pure type can exist, because a dominant attitude never fully suppresses its opposite — only outweighs it.

The MBTI takes that spectrum and hands you a definitive four-letter verdict. The theory’s own author had already ruled out the certainty the product sells.

Here is the part that decides the whole argument, and it is a question about the shape of data, not about anyone’s opinion.

If people genuinely divide into introverts and extroverts as separate kinds, then plotting everybody’s scores should produce two distinct humps with a gap between them — a bimodal distribution. Think of measuring the height of a mixed group of adults, then splitting them by sex: you get two overlapping curves with visibly different peaks. That is what a real category looks like in data.

MBTI scores do not do this. They pile up in the middle. The distribution is centre-weighted, which is exactly what you see when you measure a continuous trait rather than a pair of categories.

Early studies did report bimodal humps, and supporters cited them for years. Then researchers re-scored a sample of around 12,000 people and found those humps were an artefact of the statistical settings used — a default parameter in the scoring software. Increase the precision, and the humps flatten into a single central peak.

So the test draws its line through the fattest part of the curve, where nearly everyone actually sits, and does it four separate times. If your score sits near a boundary — and most people’s do — then the letter you are assigned rests on a handful of answers that could easily have gone the other way.

Which produces the failure everybody has noticed personally.

Studies of retest stability find that somewhere between 39 and 76 per cent of people are assigned a different four-letter type when they sit the questionnaire again within five weeks. Five weeks. Your personality did not change. The instrument simply landed on the other side of a line you were always standing on.

In 1991 a committee convened by the US National Academy of Sciences reviewed the evidence and concluded there was not sufficient, well-designed research to justify using the MBTI in career counselling. The report noted that the claims made for the instrument ran ahead of the research supporting them. Thirty-five years on, no comparable review has overturned that finding.

Meanwhile, the alternative that academic psychology actually uses — the five-factor model, usually called the Big Five — reliably predicts things the MBTI does not, including job performance.

This is where honesty requires slowing down, because the case against Myers-Briggs is routinely overstated, and the overstatement is itself a myth.

The MBTI is not measuring nothing. Its extraversion scale correlates at around 0.74 with the Big Five’s extraversion measure — a strong relationship. It is picking up real variation in real people. The problem is not the raw signal. It is the decision to chop that signal into binary letters.

The publisher, now called The Myers-Briggs Company, also does not defend the uses that make critics angriest. It states plainly that using the MBTI for hiring or selection is inappropriate — and it has been noted that such use may not survive legal scrutiny of employment testing. Every organisation screening candidates by four-letter type is doing something the manufacturer tells them not to do.

And the company disputes the reliability figures. Its own research on the current commercial version reports test-retest correlations of 0.81 to 0.86 across the four scales over intervals of one to fifteen weeks.

Both numbers can be true at once, and the reason is worth understanding, because it is the crux of the entire dispute. The company reports correlations on the underlying continuous scores. Critics report how often the resulting category flips. A person can sit in almost exactly the same place on the scale both times — a high correlation — and still cross the dividing line and be handed a different type. The scale is reasonably stable. The label sitting on top of it is not. When a company reports scale correlations in answer to a complaint about type flipping, it is answering a question nobody asked.

There is one more structural problem, and readers of this newsletter will find it familiar.

A large share of the published research supporting the MBTI’s validity has come from the Center for Applications of Psychological Type — an organisation founded in association with the Myers-Briggs Foundation — and appeared in that centre’s own journal, the Journal of Psychological Type.

The body producing the favourable evidence, the journal publishing it, and the interests served by the conclusion are not independent of one another. That does not automatically make the findings wrong. It does mean the evidence base is not what it looks like from the outside, and it is the same pattern this newsletter has documented in sugar research and in tobacco science.

None of this has dented the product, and the reason is not stupidity on the part of the people who take it.

Every one of the sixteen descriptions is flattering. There is no type that says you are unreliable, or cruel, or dim. The model has no dimension for emotional stability at all — neuroticism, the Big Five factor that most strongly predicts mental health outcomes, is simply absent. Nothing can come back negative.

The descriptions are also broad enough to fit almost anybody, which is the Barnum effect: statements calibrated so that nearly everyone reads them and thinks, that is remarkably accurate. This is the same machinery that powers horoscopes, and it produces the same jolt of recognition.

And in an office, a four-letter code is a socially safe way to talk about personality. Nobody is offended by being told they are an ENFP. That utility is real — but it is the utility of a shared vocabulary, not of a measurement.

Origins and biography: Merve Emre, The Personality Brokers: The Strange History of Myers-Briggs and the Birth of Personality Testing (2018), reviewed in The New York Review of Books and Bookforum; Wikipedia biographical entries on Katharine Cook Briggs and Isabel Briggs Myers; The Myers-Briggs Company and Truity histories of the instrument’s development, Form A, the 1943 launch price and the Office of Strategic Services order.

Jung’s own position: C. G. Jung, Psychological Types (Collected Works Vol. 6, 1921), §6 and §563; Richard Evans, Conversations with Carl Jung (Jung–Evans conversations, p. 23–24); Jung, Letters Vol. II, pp. 550–552.

Distribution and type structure: Robert J. Harvey and Tammy L. Bess, “Bimodal Score Distributions and the Myers-Briggs Type Indicator: Fact or Artifact?” (Journal of Personality Assessment, 2001/2002), re-scoring approximately 12,000 respondents; 80,000 Hours technical review of the MBTI.

Reliability and validity: David J. Pittenger, “Measuring the MBTI… And Coming Up Short” (Journal of Career Planning & Employment, 1993) and “Cautionary Comments Regarding the Myers-Briggs Type Indicator” (2005); Gregory J. Boyle, “Myers-Briggs Type Indicator: Some Psychometric Limitations” (Australian Psychologist, 1995).

The 1991 review: Daniel Druckman and Robert A. Bjork (eds.), In the Mind’s Eye: Enhancing Human Performance, National Research Council / National Academy of Sciences (1991), chapter 5, pp. 99–100.

Publisher’s position: The Myers-Briggs Company, MBTI Facts and Validity & Reliability pages; MBTI Manual for the Global Step I and Step II Assessments, 4th ed. (2018), reporting test-retest coefficients of 0.81–0.86; the company’s published statistics on Fortune 500 usage, 115 countries and 29 languages.

Independence of the evidence base: Wikipedia’s Myers–Briggs Type Indicator entry, documenting the role of the Center for Applications of Psychological Type and the Journal of Psychological Type; Annie Murphy Paul, The Cult of Personality Testing (2004); Adam Grant’s published critiques.

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