Can the 16 types be extended to 64?

Yes, and doing it properly also fixes the biggest scientific problems with four-letter types.

1. What the four letters actually measure

When researchers gave people both the MBTI and a Big Five inventory, the four MBTI scales lined up with four of the Big Five traits. E/I matched Extraversion and S/N matched Openness, both strongly. T/F matched Agreeableness and J/P matched Conscientiousness, both moderately. The fifth Big Five trait, Neuroticism (the reverse of Emotional Stability), had no MBTI counterpart.[1] So the 16 types are a coarse view of four real traits, with one major trait missing.

2. The two missing letters

Emotional Stability (C/R) is one of the most consequential traits measured. It is the strongest personality predictor of wellbeing and job satisfaction, and it is closely linked to anxiety and depression.[29][10][30]

Honesty-Humility (M/A) is the sixth factor found in lexical studies across many languages, which led to the HEXACO model.[5] It predicts ethical behaviour, cooperation and workplace deviance beyond the Big Five.[13][14][6]

Six traits, each split high or low, give 2⁶ = 64 types. Every letter is backed by decades of research.

3. Fixing the “my type changed” problem

A long-standing criticism of four-letter tests is that many people get a different type on retest. Scores pile up near the middle, so small fluctuations flip letters.[2] We report a percentile for every trait and flag any trait within 10 points of average as borderline, along with the type you could plausibly get instead.

4. Items and norms

All 62 items come from the public-domain International Personality Item Pool, which is free for any use including commercial. They are the 50-item Big-Five factor markers[3] plus 12 IPIP-HEXACO Honesty-Humility items[4], three per facet (Sincerity, Fairness, Greed Avoidance, Modesty). The 12 were chosen for the highest item-total correlations.

TraitItemsNorm NReliability (α)Mean (1–5)SD
Extraversion1019,7180.893.010.92
Openness / Intellect1019,7180.793.910.63
Agreeableness1019,7180.833.850.71
Conscientiousness1019,7180.813.350.73
Emotional Stability1019,7180.872.900.86
Honesty-Humility1222,7820.823.390.70

Norm samples: Open Psychometrics public datasets of online volunteers, collected around 2012 (Big Five: N = 19,718; IPIP-HEXACO: N = 22,782). The Honesty-Humility norms were collected on a 7-point scale and linearly rescaled to our 5-point scale. Online volunteer samples skew young (median age ≈ 22) and English-speaking. We plan to re-norm on our own users and publish the results.

5. The Deep Report (29 facets)

The optional Deep test uses the public-domain IPIP-NEO-120, which measures 30 facets of the Big Five with 4 items each (Johnson, 2014, Journal of Research in Personality, 51, 78–89). We omit the Liberalism facet because its items ask about voting for liberal or conservative candidates. Percentiles come from Johnson’s public dataset (410,376 complete responses), and facet reliabilities there range from α = 0.66 to 0.88. Facets are less precise than the six broad traits, so the report says so.

6. Limitations, stated plainly

  • Self-report reflects how you see yourself. It is not a clinical, diagnostic or hiring instrument.
  • Traits are continuous. A type is a summary, and two people with the same code can differ a lot in their percentiles.
  • Trait–outcome links are real but modest (typically r ≈ .10–.30). They replicate well, but with smaller effects than first reported.[37][34][38]
  • Personality changes. People tend to become more conscientious, agreeable and emotionally stable with age, and deliberate effort or therapy can change traits.[33][35][36]
  • The four-letter names are our own trait-based descriptions. We do not use, and make no claims about, “cognitive functions”, which lack empirical support.

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