Stuff You Should Know

Selects: How Personality Tests Work

November 15, 2025

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  • The effort to categorize human personality, exemplified by the Myers-Briggs Type Inventory (MBTI), stems from psychology's early need to establish itself as a legitimate science through quantification. 
  • The MBTI is heavily criticized by the scientific community because it is based on Carl Jung's non-empirical theories and forces complex human traits into rigid, non-spectrum-based dichotomies. 
  • Historically, personality categorization began with ancient concepts like the four humors, demonstrating a millennia-long human desire to simplify complex personalities into distinct 'types.' 
  • Personality assessments that rely on universally positive statements, such as having "unused potential," are highly likely to be rated as accurate by recipients, even if the assessment is identical for everyone (demonstrating the Barnum effect). 
  • A significant portion of people (around 15% in the example discussed) will reject a universally positive personality assessment as inaccurate, suggesting they are more self-aware or less susceptible to flattering generalizations. 
  • The podcast listeners of *Stuff You Should Know* frequently report that the show helps them manage anxiety, often by encouraging them to abandon guilt associated with productivity and embrace relaxation, sometimes alongside lifestyle changes like abandoning television. 

Segments

Introduction to Personality Tests
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(00:00:49)
  • Key Takeaway: The MBTI is extremely widespread in corporate America, with high usage among Fortune 100 companies.
  • Summary: The segment begins with advertisements before Josh Clark introduces the topic of personality tests, specifically noting the ubiquity of the MBTI in corporate settings. He mentions that a significant percentage of companies in America, including 89 of the Fortune 100 (as of a 2001 statistic), utilize the inventory. The episode promises to cover tests ranging from the Rorschach to the MBTI, with the latter being the primary focus due to its popularity.
Ancient Personality Categorization
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(00:06:26)
  • Key Takeaway: The concept of personality typing dates back to ancient theories linking temperament to the four bodily humors: black bile, yellow bile, phlegm, and blood.
  • Summary: The hosts trace the history of personality categorization back to the four humors, which were believed to cause disease when imbalanced. These humors were linked to corresponding personality types, such as ‘melancholy’ being associated with black bile. This ancient system established the foundational idea that human personality could be reduced to a single, definable type, a concept criticized for oversimplifying human complexity.
Jung’s Psychological Types
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(00:09:59)
  • Key Takeaway: Carl Jung’s 1921 book, Psychological Types, introduced the foundational concepts of sensation, intuition, thinking, and feeling, which underpin most modern personality tests.
  • Summary: Carl Jung is credited with laying the groundwork for modern personality classifications through his book, Psychological Types. He established four core categories: sensation, intuition, thinking, and feeling, which are modified by whether a person is introverted or extroverted. Although Jung’s ideas were based on deep thought rather than empirical data, his concepts of introversion and extroversion remain widely accepted in psychology.
Rise of Quantifiable Psychology
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(00:14:01)
  • Key Takeaway: The urgent need to establish psychology as a science drove a movement to quantify personality, contrasting with the ‘mushy’ psychoanalytic approach.
  • Summary: A parallel movement in psychology sought to quantify human traits, inspired by figures like Alfred Binet (father of the IQ test), to prove psychology’s scientific basis. This drive led Catherine Cook Briggs and her daughter, Isabel Briggs Myers, to develop the MBTI post-World War II to help place women entering the workforce into suitable jobs. They built upon Jung’s work, notably stripping away concepts related to the unconscious.
MBTI Structure and Cost
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(00:30:46)
  • Key Takeaway: The MBTI sorts individuals into 16 types based on four dichotomies: Introversion/Extroversion, Sensing/Intuition, Thinking/Feeling, and Judging/Perceiving.
  • Summary: The MBTI inventory sorts people based on which side of four dichotomies they prefer, such as Sensing (liking empirical data) versus Intuition (going with gut feeling). Judging (preferring schedules) and Perceiving (being flexible) form the final pair, similar to Type A/Type B concepts. Taking the test costs about $50, with extra fees for feedback or career reports, and administering it requires expensive certification from the publisher, CPP.
Scientific Critique of MBTI
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(00:41:47)
  • Key Takeaway: The MBTI is widely criticized for lacking scientific validity, as its dichotomies fail to account for personality existing on a spectrum, leading to inconsistent results.
  • Summary: A major criticism is that the MBTI’s four dichotomies are problematic because personality traits exist on a spectrum, not as binary choices; people near the middle can flip types easily. Furthermore, the test was constructed backward, with the types created first, followed by the instrument designed to detect them, violating standard scientific methodology. The MBTI’s reliance on self-reporting also introduces inherent bias.
Rorschach and MMPI Comparisons
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(00:50:10)
  • Key Takeaway: The Rorschach inkblot test is notorious for wildly inaccurate results, often labeling mentally sound individuals as psychotic, while the MMPI relies on a potentially flawed ‘sane’ control group baseline.
  • Summary: The Rorschach test is highly subjective, though some adherents claim movement seen in the blots correlates with depression. A 2000 study showed a high percentage of mentally sound children were labeled borderline psychotic by the test, yet it is still used in legal settings. The MMPI, while better at detecting faking, is criticized for being too invasive and basing its results on a control group representing mid-century Minnesota normalcy, perpetuating oppressive groupthink.
The Forer Effect in Testing
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(00:59:48)
  • Key Takeaway: Many personality tests, like the MBTI, rely on the Forer effect, providing universally positive statements that people readily accept as accurate self-assessments.
  • Summary: Skeptics compare personality tests to astrology because they often employ positive psychology, ensuring users rarely walk away feeling bad about themselves. This relates to the Forer effect, where subjects rate generalized, flattering personality assessments as highly accurate, even when everyone receives the identical description. This effect highlights the human desire to identify with positive, non-critical labels.
Barnum Effect in Testing
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(01:00:53)
  • Key Takeaway: Flattering personality assessments, even generic ones, achieve high accuracy ratings because recipients want to identify with the positive traits described.
  • Summary: Assessments that contained only positive statements, such as having unused potential, were favorably received. When the same generic assessment was given to an entire class, it achieved an 85% accuracy rating. Only about 15% of the class rejected the assessment as inaccurate.
Podcast Wrap-up and Promotion
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(01:01:55)
  • Key Takeaway: Listeners can find more information on personality tests by searching the archives at houseofworks.com.
  • Summary: The hosts express satisfaction with covering the topic of personality tests, which was a special request. Listeners interested in personality tests are encouraged to search for related content online or on the show’s website. The segment concludes by transitioning into listener mail.
Listener Mail: Anxiety and Productivity
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(01:02:27)
  • Key Takeaway: Abandoning the modern obsession with constant productivity and embracing relaxation can significantly improve mental health and reduce anxiety levels.
  • Summary: A listener shared that realizing the guilt associated with productivity is a modern phenomenon helped them manage anxiety. Listening to the Stuff You Should Know podcast during walks contributed positively to their improved mental health. The listener also noted that abandoning television viewing aided in tackling anxiety.
Listener Mail: TV Effects Inquiry
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(01:03:51)
  • Key Takeaway: The introduction of television in Bhutan correlated with a reported 700% increase in the country’s crime rate, suggesting a potential negative societal effect.
  • Summary: A listener inquired about research concerning the effect of television on lives, noting that watching TV did not help their anxiety. They recalled reading that after TVs became mainstream in Bhutan, the crime rate rose substantially. This topic was suggested as a potential future episode for Stuff You Should Know.
Show Credits and Sponsorships
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(01:04:24)
  • Key Takeaway: Listeners can contact the show via email at stuffpodcast at iHeartRadio.com, and the program is a production of iHeartRadio.
  • Summary: The hosts thanked the listener for their feedback, noting that many listeners report the show helps with anxiety. Contact information for listener mail was provided, along with details about the show’s production company. The segment concluded with advertisements for Capital One and Duracell batteries.