What the four letters of your type mean

The idea of personality types goes back to the Swiss psychiatrist Carl Jung. In Psychological Types, first published in German in 1921 and in English in 1923, he wrote that "two types especially became clear to me which I have termed the Introversion and the Extraversion Types."

Jung described the difference as one of direction. The introverted attitude "sets the self and the subjective psychological process above the object", while the extraverted attitude "sets the subject below the object". In plain words: one turns first to the inner world of thoughts and feelings, the other to the outer world of people and things.

He also described four basic ways the mind works: "there exist thinking, feeling, sensation, and intuition." Two of our scales grow from these. Sensation and intuition became a scale about how you take in information, and thinking and feeling became a scale about how you make decisions.

• Energy, E or I: where you tend to recharge. Extraverts tend to recharge around people and think out loud; introverts tend to recharge with time alone and think before they speak.
• Information, S or N: what you tend to trust. Practical types lean on facts, details and hands-on experience; imaginative types lean on hunches, patterns and possibilities.
• Decisions, T or F: how you tend to choose. Thinking types weigh logic and honest feedback; feeling types weigh how the people involved will be affected.
• Lifestyle, J or P: how you tend to organize your days. Planned types like lists and settled decisions; spontaneous types keep their options open and enjoy a late change of plan.

Every one of these describes a tendency, not a rule. An introvert can love a party, and a planner can enjoy a free afternoon. The letter says which way you lean when you have a choice.

The test has 32 statements, eight for each scale. On every scale, four statements lean toward one side and four toward the other, so the wording itself doesn't push you either way. You say how much you agree with each one on a five-point scale.

Each answer moves its scale a little toward one side. The letter goes to whichever side ends up ahead, and your result shows how far ahead as a share, such as 63% Introvert. In the rare case of an exact tie, your last answer on that scale that wasn't neutral decides it.

When the winning side has 55% or less, your result says so: "Close to the middle, so both sides may sound like you." That note matters more than the letter above it.

Jung himself was clear that nobody is purely one type. He wrote that "every individual possesses both mechanisms", and that a type is only "the relative predominance of the one or the other". In his words, "there can never occur a pure type".

Our scores reflect that. A result of 53% Introvert is not a smaller version of 100% Introvert. It means your answers came out almost even, and with only eight statements per scale, one or two different answers could move it to the other side on another day.

The same goes the other way. Two people who both get an I can be very different: one at 53% and one at 97% share a letter but not much else on that scale. The four letters are a summary, and a summary always drops detail.

If one of your scales is close to the middle, read the descriptions for both letters. You will probably recognize yourself in each.

Much of today's personality research describes people with traits measured along continuous scales rather than with types. The best-known set is the five-factor model, often called the Big Five. Robert McCrae and Oliver John summarize it as five basic dimensions: "Extraversion, Agreeableness, Conscientiousness, Neuroticism, and Openness to Experience."

The model came out of the words people use to describe each other. Goldberg traces the work back to Raymond Cattell, who began with English trait terms some 45 years earlier. In one of the key studies, Goldberg grouped 1,431 trait adjectives into clusters and found "virtually identical structures" across 10 different ways of analyzing them. When he looked for more than five factors, none of the extra ones held up across samples. McCrae and John add that the evidence supports the model's applicability "across observers and cultures".

McCrae and John also describe the model as a "hierarchical organization of personality traits": each broad dimension holds narrower facets. Extraversion, for example, includes both a taste for taking charge and a taste for lively company, and a person can be high on one and lower on the other.

The two approaches overlap. Our Energy scale is closest to extraversion. The difference is in what each keeps: a trait score keeps your exact position on the scale, while a type keeps only the side you landed on. That is why our result shows the share behind every letter, not only the letter.

Personality is fairly stable, but it isn't fixed. In a meta-analysis of 92 samples followed over time, Brent Roberts, Kate Walton and Wolfgang Viechtbauer found that people tend to change in steady, shared ways across life.

• People increase in social dominance, a facet of extraversion, and in conscientiousness and emotional stability, especially between about 20 and 40.
• Social vitality, another facet of extraversion, and openness rise in adolescence and then decline in old age.
• Agreeableness changed only in old age.

Gender made little difference to these patterns. Longer studies, and studies of people born more recently, showed more change. So if you take the test again in a few years, a close scale may well come out the other way, and even a clear one can soften. That is a sign the test is describing you as you are now, which is all it claims to do.

• Look at the bars, not only the letters. A 91% lean and a 53% lean say very different things.
• For any scale marked as close to the middle, read both letters' descriptions and keep the parts that fit.
• Answer the statements as you usually are, not as you'd like to be or as you are at work.
• If you take it again, leave a few months between tries, and compare the bars rather than only the letters.
• Use your type for reflection and conversation, never to judge or sort other people.

This test is for self-reflection and fun. It describes tendencies, not fixed facts about you, and it isn't a professional assessment.