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I'm Lavena Xu-Johnson. I write about psychology for founders. Why? Because scaling a business means scaling ourselves first.

Happy Wednesday, founders,

“What’s your MBTI?”

This became one of the most common questions I encountered after meeting someone new for 20 mins in the past few years…

In case you don’t know: MBTI, or Myers-Briggs Type Indicator, is a personality assessment developed by a mother-daughter duo - Katharine Cook Briggs and Isabel Briggs Myers, based on Carl Jung’s 1921 book Personality Types, during World War II.

The Myers-Briggs Type Indicator is not only used by your friends and your next-door TikTok influencer. It has been widely adopted by 88 of the Fortune 100 companies, including E&Y, Marriott, IBM, and by about 200 U.S. government agencies, schools (I first had mine done in high school), the Department of Defense, and the CIA for decades.

But when I come across a ‘fortune-teller’ who seems confident decoding people based on if they’re an ‘E’ person (Extraversion) or an ‘I’ person (Introversion), or a ‘F’ (Feeling) or ‘J’ (Judgement), I can’t help becoming more skeptical on how this tool is being used or mis-used in social settings.

We’re complex individuals. Can we really fit into 16 rigid boxes? Should friends, employers, schools, and the government judge us based on four letters that are supposed to indicate our behaviour? Or have we, the users, completely misinterpreted the original intent and the proper way to use it?

Behind the theory and framework is a story of two women’s life-long devotion to understanding personality, born from a place of compassion - a mother trying to understand her son-in-law to avoid losing her daughter.

It’s long overdue that I delve into the history, background, scientific reliability and validity, and research behind this infamous Myers-Briggs personality indicator and its $2 billion personality assessment industry.

Let’s dive in.

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The MBTI® is a forced-choice questionnaire (usually 90–100 items for the basic Step I; advanced versions have 140–180) where you pick the statement that best fits you (on a scale). Questions look like: “I like to try to innovate’ versus ‘I like to use trusted methods.’ or ‘I make decisions with my heart.’ versus ‘I make decisions in my head.’

Your answers indicate a preference on each of the four dimensions (E–I, S–N, T–F, J–P), which combine into one of 16 four-letter types (e.g., ENTP, ISFJ). Official MBTI results use these four-letter types; from there, you can read a type description to explore likely strengths, blind spots, and how you prefer to communicate, make decisions, and work - useful input for career and team development.

The four dimensions of MBTI:

If you’ve never taken the MBTI, the official site is here (or take a free one here).

When used with care, MBTI gives us language for the ways we naturally pay attention, decide, and organise - so instead of misreading each other’s intent, we allocate tasks that may be better fits to our team’s strengths. It lowers the temperature in hard weeks: instead of “why are you like this?”, we ask “what does your preference need here?”

Green lights

Red flags (misuses)

In the 1920s, Katherine Cook Briggs (born 1875), a mother, the wife of an engineer and physicist, and a child prodigy who entered college at age 13 (one of the nine women among 100 men), finally found her intellectual outlet after years as a homemaker. Driven by a natural curiosity about healing and human behaviour, she began working as a magazine writer on children’s education, a teacher, and an aspiring fiction writer.

As a novelist fascinated by the puzzle of the psyche, she was intrigued by Carl Jung’s book, Psychological Types. That curiosity intensified when her only daughter married someone she struggled to understand. Rather than judging him and fearing a rift with her daughter, she began researching personality in the hope of quantifying what that difference might be.

In 1923, Katherine started to correspond with Carl Jung by letter, and eventually met in the U.S. To support her work, Jung shared personal notes on type theory.

Isabel Briggs Myers, her daughter, was a successful mystery novelist who paid little attention to personality types until World War II. Wanting to contribute beyond volunteering as a nurse, she became fascinated by the Humm-Wadsworth temperament scale and took a role in the personnel department of the Pennsylvania Company for Banking and Trusts, which used the assessment on their employees. Unsatisfied with its data, effectiveness, and especially its judgmental ‘bad’ or ‘good’ scoring, she envisioned a new instrument that described differences without negative labels.

The mother-daughter duo began their work with one mission: match people to roles to reduce misfit and increase job satisfaction. Building on Katharine’s decades of study, Isabel drafted hundreds of items, and finalised on 172 questions after collecting data from people around them - starting with her son’s high school classmates, then soon adopted by George Washington University’s Medical schools. The first prototype of the Myers-Briggs Type Indicator was born.

The family was soon connected with the Educational Testing Service (ETS), publisher of major psychometric assessments, and also the SAT. Although ETS supported further development, they never published MBTI - their statisticians were skeptical of its test-retest results - over 50% of the participants who took the test had a different result when they took it the second time.

Despite setbacks, they pushed on as women working at the edges of academia at a time when women’s ideas were rarely taken seriously. Isabel’s first client turned out to be the Office of Strategic Services (OSS), the forerunner of the CIA, a group of wartime psychologists who deployed the indicator to match the covert operative to secret missions best suited to their personalities during World War II.

In 1975, Isabel signed with Consulting Psychologist Press (now the Myers-Briggs Company), which grew MBTI into its bestselling product, and it remains to be MBTI’s sole publisher today.

It’s no secret that the MBTI has drawn plenty of criticism, especially from personality researchers. As Professor Haslam notes, much of the pushback comes from the tool’s very appeal - it’s intuitive, accessible, and (some argue) overly simple. One of the most-cited critiques is David J. Pittenger’s 2005 article.

With that in mind, here are the major criticisms and counterpoints to each:

However: They were highly educated and intelligent individuals and devoted their entire lives to personality type research. Myers received mentorship and support from figures such as Edward N. Hay and Donald MacKinnon (UC-Berkley’s Head of the Institute of Personality and Social Research). This study also shows that without formal psychology training can create personality scales as valid as professionally developed ones.

However: Carl Jung’s type theory stands apart from his other theories, and the concepts of introversion and extraversion have been highly respected and established in empirical research.

However: It’s true that MBTI scores are continuously distributed, and most people fall near the middle. But not all type models are weak; some are robust and widely validated - most notably John Holland’s RIASEC model in vocational psychology.

However: MBTI has 70+ years of research and application, and like any self-report tool, its reliability varies by sample and context, not because the instrument “has” a single reliability. Yes, some studies report weak coefficients, but many show strong ones: a meta-analysis by Capraro (2002) found overall internal consistency around .80–.87 (with more variation on Thinking–Feeling, .64–.87), which meets common psychometric guidelines (≥ .70). Such variability is normal - Gnambs (2016) even showed the same Big Five measure can look reliable in one sample and not in another - so absolute claims are risky. On validity, Moyle & Hackston (2018, Journal of Personality Assessment) address common critiques and argue for experiential validity alongside traditional evidence.

Coming back to my original curiosity: Is MBTI ‘valid enough’ to guide us on our personality and job fit?

In my opinion, that is the wrong question to begin with. First, it is an indicator, not a test, a fact explicitly stated in the name and emphasized by MBTI practitioners. Second, it was never designed to predict job performance; it’s meant to help us recognise the kinds of work that satisfy our own preferences and to increase self-awareness from within. If an institution uses any personality measure to make a hard gatekeeping decision, it risks structural discrimination, but that’s a misuse by users, not the tool’s intent.

Isabel Myers’ conviction lies in her hope that the indicator could show people their gifts, and help them understand how they might add value and contribute to the world. “She hoped the indicator could help prevent another Hitler,” Myers’ granddaughter Kathleen Hughes, a journalist, recalls in the book Gifts Differing, “by giving as many people as possible a greater understanding and respect for individual differences.”

I loved writing this one, I hope it was as fun to read.

With deep respect to Myers and Briggs.

Until next week,
Lavena

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