Here is a sentence that is true: a personality assessment used by 88% of Fortune 500 companies, taken by over 2.5 million people per year, generating an estimated $2–4 billion in annual revenue, administered by thousands of certified practitioners...
In This Chapter
Chapter 7: Myers-Briggs, Enneagram, and the Personality Test Industry — What Actually Measures Personality?
Here is a sentence that is true: a personality assessment used by 88% of Fortune 500 companies, taken by over 2.5 million people per year, generating an estimated $2–4 billion in annual revenue, administered by thousands of certified practitioners worldwide, and cited in countless team-building exercises, leadership programs, and career guidance sessions — has no meaningful test-retest reliability and no demonstrated predictive validity for job performance.
That assessment is the Myers-Briggs Type Indicator (MBTI).
Here is another sentence that is true: a personality framework that has been replicated across dozens of cultures, predicts real-world outcomes including academic performance, job performance, health behaviors, and relationship satisfaction, and is the consensus model among personality researchers — is almost never used in corporate settings and is virtually unknown to the general public.
That framework is the Big Five (OCEAN: Openness, Conscientiousness, Extroversion, Agreeableness, Neuroticism).
This chapter is about the gap between these two realities — between what the personality test industry sells and what personality science supports. It's a gap worth understanding, because personality assessments shape how millions of people think about themselves, their relationships, and their careers. When those assessments are wrong, the consequences are real.
Before You Read: Confidence Check
Rate your confidence (1–10) that each statement is true.
- "The Myers-Briggs Type Indicator (MBTI) is a scientifically valid personality assessment." ___
- "Your MBTI type reveals important truths about your personality." ___
- "The Enneagram has a solid scientific basis." ___
- "If 80%+ of Fortune 500 companies use MBTI, it must work." ___
- "There is no scientifically valid way to measure personality." ___
The Myers-Briggs Type Indicator: A $2 Billion Industry Without Evidence
The Origin Story
The MBTI was developed in the 1940s by Katharine Cook Briggs and her daughter, Isabel Briggs Myers. Neither was a psychologist. Katharine Briggs was a homemaker with an interest in personality; Isabel Myers had a degree in political science. Their instrument was inspired by Carl Jung's 1921 book Psychological Types, which proposed that people differ on dimensions of perception (sensing vs. intuition) and judgment (thinking vs. feeling), and on the direction of their energy (introversion vs. extroversion).
Jung himself never intended his typology to be used as a classification system. He wrote: "Every individual is an exception to the rule." He described the types as idealizations, not as boxes people fit neatly into. The MBTI took Jung's fluid, nuanced descriptions and hardened them into a 16-type system with four-letter codes: INTJ, ENFP, ISFJ, and so on.
The Psychometric Problems
The scientific problems with the MBTI are well-documented and widely agreed upon among personality researchers:
Poor test-retest reliability. If you take the MBTI today and retake it in five weeks, there is approximately a 50% chance you will be classified as a different type. This is not what reliable measurement looks like. A thermometer that gave you a different reading every time you checked your temperature would not be considered a useful thermometer.
The reason for this instability is structural: the MBTI forces continuous dimensions into binary categories. If you score 51% toward "Thinking" and 49% toward "Feeling," you're classified as a "T." If you score 49% toward "Thinking" and 51% toward "Feeling" — a trivially small difference — you're classified as an "F." Because most people score near the middle on each dimension, small fluctuations in their responses produce different type assignments.
No evidence for discrete types. The MBTI assumes that people fall into 16 distinct types. But when you look at the actual distribution of scores, they don't cluster into types — they form a continuous bell curve on each dimension, just like the introversion-extroversion spectrum we discussed in Chapter 6. There are no natural "types" in the data. The types are imposed by the scoring system, not discovered in the personality.
Poor predictive validity. The gold standard for any assessment is: does it predict anything useful? In the case of the MBTI, the answer is: barely. Multiple reviews have found that MBTI types do not meaningfully predict job performance, career satisfaction, team effectiveness, or any other workplace outcome that companies care about.
A 1991 review by the National Research Council concluded: "There is not sufficient, well-designed research to justify the use of MBTI in career counseling programs." That assessment has not substantially changed in the subsequent three decades.
Incomplete personality coverage. The MBTI measures four dimensions. The Big Five measures five. The dimension missing from the MBTI? Neuroticism (or emotional stability) — arguably the most important personality dimension for predicting mental health, relationship quality, and job performance. The MBTI simply doesn't measure one of the most consequential aspects of personality.
Why It Persists: The $2 Billion Answer
If the MBTI is psychometrically unsound, why is it used by 88% of Fortune 500 companies? Why do 2.5 million people take it every year? Why has it generated a multi-billion-dollar industry?
The answer connects directly to everything we've learned in Part I:
The Barnum effect. MBTI type descriptions are carefully crafted to be flattering and broadly applicable. "INTJs are strategic thinkers who value competence and independence" — who wouldn't want to be described this way? The descriptions feel accurate because they're designed to feel accurate, not because they capture meaningful individual differences.
Identity and community. Your MBTI type provides an identity label, a community (r/INTJ has over 170,000 members), and a vocabulary for talking about yourself. "I'm an INTJ" is socially useful regardless of whether it's psychometrically meaningful. The identity value drives adoption independent of the scientific value.
Institutional momentum. Once a company has invested in MBTI certification, training materials, and practitioner networks, switching to a different assessment requires writing off that investment and retraining staff. Sunk costs keep the MBTI in place.
The certification industry. Becoming a "certified MBTI practitioner" requires paying the Myers-Briggs Company for training. These certified practitioners have a financial interest in the continued use of the instrument. The certification creates a network of advocates with aligned incentives.
It's fun. MBTI workshops are enjoyable. People like talking about their types, comparing themselves to others, and having their personality validated. Participant satisfaction (Kirkpatrick Level 1, as we discussed in Chapter 5) is high. And as long as evaluation stops at "did participants enjoy it?", the MBTI looks successful.
The Enneagram: Even Less Evidence, Even More Growth
If the MBTI has poor psychometric properties, the Enneagram has essentially none.
The Enneagram is a nine-type personality system with origins that are variously attributed to the Sufi tradition, the teachings of George Gurdjieff, and the work of Oscar Ichazo and Claudio Naranjo in the 1960s–70s. Its spiritual and philosophical roots are explicit — the Enneagram was originally presented as a tool for spiritual growth, not as a scientific personality model.
Despite this, the Enneagram has experienced explosive growth in the 2020s, particularly among millennials and Gen Z. Enneagram-related content generates millions of views on TikTok. Enneagram-based coaching is a growing industry. Several bestselling books (including The Road Back to You and The Wisdom of the Enneagram) have brought the system to mainstream audiences.
The Evidence Problem
The scientific evidence for the Enneagram is extremely thin:
No consistent factor structure. When Enneagram assessments are subjected to factor analysis (the standard technique for determining whether a personality inventory measures what it claims to measure), the results do not consistently produce nine distinct factors. The nine types don't appear as natural clusters in the data.
Poor psychometric properties. Studies that have examined Enneagram instruments find low internal consistency, poor test-retest reliability, and limited evidence of construct validity. The few studies that exist have generally used small samples and weak designs.
No demonstrated predictive validity. There is no body of research showing that Enneagram types predict job performance, relationship quality, mental health outcomes, or any other real-world variable.
The evidence that does exist is mostly from advocates. Most published studies on the Enneagram come from researchers who are already invested in the system. Independent, skeptical evaluations are rare and generally unfavorable.
Why It's Growing Anyway
The Enneagram's growth is driven by the same forces as the MBTI's persistence, with an additional factor:
Depth of narrative. The Enneagram offers richer, more detailed type descriptions than the MBTI. Each type has a core motivation, a core fear, a direction of growth, and a direction of stress. The narratives feel psychologically profound — which is a feature of the Barnum effect at high resolution, not of scientific validity.
Spiritual framing. The Enneagram's spiritual roots give it a different cultural niche than the MBTI. It appeals to people who are looking for self-understanding that goes beyond "personality" into meaning, purpose, and growth. This framing makes it resistant to scientific critique — if the Enneagram is "spiritual," then scientific evidence is seen as beside the point.
Social media virality. Enneagram content is even more viral than MBTI content because the nine types provide more diversity of content, more relationship-combination possibilities (Type 2 + Type 8, etc.), and more meme material.
What Actually Measures Personality: The Big Five
In contrast to the MBTI and Enneagram, the Big Five personality model (also called the Five-Factor Model or OCEAN) has robust empirical support:
Consistent factor structure. When personality questionnaire data from large samples are subjected to factor analysis, five broad dimensions consistently emerge — Openness, Conscientiousness, Extroversion, Agreeableness, and Neuroticism. This five-factor structure has been replicated in over 50 cultures.
Good psychometric properties. Big Five inventories show reasonable internal consistency and test-retest reliability. Unlike the MBTI, the Big Five doesn't force continuous scores into binary categories — it gives you a score on each dimension.
Predictive validity. The Big Five predicts real-world outcomes: - Conscientiousness is the strongest personality predictor of job performance across occupations - Neuroticism predicts mental health difficulties, relationship problems, and lower life satisfaction - Agreeableness predicts cooperative behavior, relationship quality, and lower conflict - Extroversion predicts leadership emergence, social network size, and positive affect - Openness predicts creative achievement, intellectual curiosity, and political attitudes
Cross-cultural replication. The five factors have been found in data from diverse cultural contexts, including non-Western societies, suggesting they capture something universal about human personality variation.
Why Nobody Shares Their Big Five Results
If the Big Five is superior, why hasn't it gone viral? The answer is instructive:
It's not a type. The Big Five gives you scores on five dimensions. "I'm high in conscientiousness and openness, moderate in extroversion, low in neuroticism, and moderate in agreeableness" is not a shareable identity. "I'm an INFJ" is.
It's not flattering. The Big Five includes neuroticism — a dimension that people generally don't want to score high on. The MBTI has no "bad" types. Every MBTI type description is positive. The Big Five is honest about the full range of personality variation, including the unflattering parts.
It lacks narrative. MBTI and Enneagram types come with stories — strengths, weaknesses, compatibility charts, growth paths. The Big Five provides dimensions and scores, not narratives. This makes it more scientific and less engaging.
It doesn't create community. There's no r/HighConscientiousness subreddit. There are no "Low Neuroticism" memes. The Big Five doesn't generate the identity-based communities that drive virality.
The gap between the Big Five's scientific validity and its cultural irrelevance is perhaps the clearest illustration in this book of the virality-accuracy trade-off (Chapter 1). The most scientifically valid personality framework is the least culturally popular, precisely because the features that make it valid (continuous dimensions, unflattering honesty, lack of narrative) are the features that make it unappealing.
Verdict: "The Myers-Briggs Type Indicator is a scientifically valid personality assessment" ❌ DEBUNKED — The MBTI has poor test-retest reliability (~50% of people get a different type on retest), no evidence for discrete personality types in the data (scores form continuous distributions, not clusters), poor predictive validity for job performance or other outcomes, and fails to measure neuroticism — one of the most important personality dimensions. The National Research Council concluded in 1991 that there was insufficient evidence to justify its use. Origin: Developed by Katharine Briggs and Isabel Myers (1940s), based on Carl Jung's Psychological Types (1921). Replication status: The MBTI's type structure does not replicate when examined with factor analysis.
Verdict: "The Enneagram has a solid scientific basis" ❌ DEBUNKED — The Enneagram has no consistent factor structure, poor psychometric properties, and no demonstrated predictive validity for any real-world outcome. The extremely limited research that exists is mostly from advocates, not independent evaluators. Its origins are spiritual/philosophical, not empirical. Origin: Attributed to various spiritual traditions; popularized by Ichazo and Naranjo (1960s–70s). Evidence base: Minimal and generally unfavorable.
Verdict: "The Big Five is a valid personality model" ✅ SUPPORTED — The Big Five has been replicated across 50+ cultures, demonstrates good psychometric properties, and predicts real-world outcomes including job performance, mental health, and relationship quality. It is the consensus model among personality researchers and the most empirically supported personality framework available. Origin: Developed through factor-analytic research by multiple independent teams (1980s–90s). Replication status: Extensively replicated across cultures and methods.
The Practical Implications
What should you do with this information?
If your company uses MBTI for hiring decisions: This is problematic. Using an assessment with no predictive validity for hiring is, at best, wasting money and, at worst, making decisions based on random noise. The Big Five (particularly conscientiousness) actually predicts job performance.
If you enjoy your MBTI type as a social identity: That's fine, as long as you recognize that it's functioning as entertainment and community, not as scientific self-knowledge. Think of it like your Hogwarts house — fun, identity-affirming, and not a serious assessment of your character.
If you're making life decisions based on your type: Reconsider. "I shouldn't apply for that leadership role because I'm an INFP" is a consequential decision being made on a psychometrically unsound basis.
If you want to understand your personality scientifically: Take a validated Big Five inventory (many are available free online through the IPIP). It won't give you a tidy label, but it will give you information that actually corresponds to measurable personality variation.
Fact-Check Portfolio: Chapter 7
If any of your 10 claims involve personality types (MBTI, Enneagram, or others), apply the toolkit: - Does the assessment have test-retest reliability? - Does it predict real-world outcomes? - Does it use categories or continuous dimensions? - Who profits from the assessment being perceived as valid?
Also ask: if you identify with a personality type, would you still identify with it if you learned the assessment doesn't measure what it claims to measure? What would that tell you about the role of identity vs. accuracy in your self-concept?
After Reading: Confidence Revisited
- "The MBTI is scientifically valid." — What are the specific psychometric problems?
- "Your MBTI type reveals important truths about your personality." — What does the test-retest data show?
- "The Enneagram has a solid scientific basis." — What does the factor analytic evidence show?
- "If 80%+ of Fortune 500 companies use MBTI, it must work." — What does corporate adoption tell you about effectiveness? (Hint: Chapter 5's Kirkpatrick levels.)
- "There is no scientifically valid way to measure personality." — What framework has been replicated across 50+ cultures?