Personality guides

The MBTI’s four scales measure real traits, but the 16 “types” are not. A balanced, sourced look at reliability, validity, retest problems and what is missing.

How each MBTI letter corresponds to a Big Five trait (McCrae & Costa, 1989), what the Big Five adds, and which test to use for what. With sources.

How to judge a personality test: reliability, test–retest stability, agreement with friends, real-world prediction, and why vague results feel accurate.

A transparent walkthrough of the 64 Types personality test: where the 62 questions come from, how percentiles are calculated, and what borderline flags mean.

Introversion and extraversion are one continuum, and most people sit near the middle. What the trait predicts for mood, work and relationships, with sources.

What conscientiousness is, what it predicts for work, school, health and longevity, how big the effects really are, and how to build more of it.

What neuroticism is, why the classic 16 types leave it out, what it predicts for mental health, work and love, and the evidence that it can change.

HEXACO adds a sixth trait, Honesty-Humility, to the Big Five. What it measures, how it differs from Agreeableness, and what research shows it predicts.

Which traits predict job performance, leadership, income and job satisfaction, how big the effects are, and how to use your profile to choose a career.

Which traits predict happier relationships, why personality similarity matters far less than people think, and what the biggest couples study found.

Which traits help people make friends, which help them keep friends, whether friends are similar, and practical tips for each personality letter.

Personality is fairly stable but not fixed. How traits change with age, therapy and deliberate effort, and why your type code may change on a retest.