MBTI, blood types, zodiac signs and saju: how they differ

“Is MBTI more accurate than blood type?” “What is the difference between zodiac signs and saju?” These questions come up whenever friends start talking about personality. MBTI, the Big Five, blood type personality, zodiac signs and saju (Korean four pillars) all promise an answer to “what kind of person am I?”, but they get that answer from completely different places.

In short, the five fall into two groups. MBTI and the Big Five are psychological tests that measure your current tendencies from questions you answer yourself. Blood type, zodiac sign and saju are cultural frameworks that read personality from information fixed at birth. In the first group, your result changes when you change; in the second, it stays the same for life.

So it helps to decide what you want to know before asking which one is right. This guide compares the five side by side, by what each looks at, how it reaches a result and how much research backs it, then sets out which to pick when you want fun and which when you want self-understanding. A deeper two-way comparison of saju and psychological tests is in the saju vs personality tests guide.

Put the five against the same yardstick and the differences become sharp. For each system, a first paragraph says what it looks at, how it reaches a result and what it is good for; a second says how much research shows it describes personality.

Big Five. It looks at five traits: openness, conscientiousness, extraversion, agreeableness and emotional sensitivity (neuroticism). Your answers are added up into a score for each trait, placed on a continuum, which makes it good for understanding your tendencies precisely or tracking change over time.

Evidence for the Big Five: the strongest of the five. It is the standard framework of personality research, and how its scores connect to real life has been tested for decades.

MBTI. It looks at four preferences: where you draw energy (E/I), how you take in information (S/N), what you base decisions on (T/F) and how you organize life (J/P). Your answers show which way you lean on each axis, giving one of sixteen types, which makes it good as a shared, light language for talking about differences.

Evidence for MBTI: moderate. The four axis scores connect meaningfully with Big Five traits, but because each score is cut in two at the middle, people near the line often see a letter change on a retake.

Blood type. It looks at the four ABO groups (Type A, Type B, Type O, Type AB), inherited from your parents and fixed for life, which makes it a light conversation topic, familiar in Korea and Japan.

Evidence for blood type: none for predicting personality. The idea began with a small 1927 survey by Takeji Furukawa in Japan and spread widely through Masahiko Nomi’s books in the 1970s, and large surveys have found no meaningful link between blood type and personality.

Zodiac sign. It looks at which of the twelve sections of the ecliptic the Sun was passing through on your birthday, that is, the twelve signs and their four elements (fire, earth, air, water). It is set by the month and day of your birth, which makes it good for birthday chat and fun such as zodiac sign compatibility.

Evidence for zodiac signs: none for predicting personality. Neither an experiment asking astrologers to match birth charts to personality test results nor research comparing many people’s birthdays with their personality scores found anything beyond chance.

Saju. It looks at four pillars that turn your birth year, month, day and hour into eight characters of the sexagenary cycle, and the five elements. It is calculated from your birth date and time, so people born on the same day in the same two-hour block share the same eight characters, and it works as a story frame for New Year plans or reflection and as cultural fun such as Chinese zodiac compatibility.

Evidence for saju: no validated evidence for predicting personality. It is a symbolic system drawn from an old calendar and philosophy, not something built as a measuring tool.

Evidence for a personality tool is usually judged on two questions. Does the same person get a similar result on a retake (reliability)? And does the result connect meaningfully with real behavior and life outcomes (validity)? A system fixed at birth passes the first automatically, because its result never changes; the problem is the second. A result that never changes is not the same as a result that is right.

The Big Five has built up the most answers to that second question. In a review pooling many studies, how well traits such as conscientiousness predicted longevity, divorce and career attainment was comparable to family socioeconomic status or cognitive ability (Roberts et al., 2007), and a large replication project that retested 78 published links between personality and life outcomes found close to nine in ten of them again (Soto, 2019), though the replicated effects were about 77% the size of the originals. That does not mean a score decides anyone’s future; it means meaningful tendencies show up when many people are pooled.

MBTI sits in the middle. Its four axis scores connect meaningfully with Big Five extraversion, openness, agreeableness and conscientiousness (McCrae & Costa, 1989), so it does measure real tendencies. But because continuous scores are cut in two to make types, critics have long pointed out that many people change at least one letter when retested a few weeks later (Pittenger, 2005). Why results change and how to read them is covered in the MBTI accuracy guide.

Zodiac signs and blood types have been tested directly. In a double-blind experiment published in Nature in 1985, astrologers given only birth charts did no better than chance at picking the matching personality test result (Carlson, 1985), and a large study comparing many people’s birthdays with their personality and intelligence scores found no differences by sign (Hartmann et al., 2006). Blood type personality began with a small 1927 survey by the Japanese educator Takeji Furukawa and spread widely through Masahiko Nomi’s books in the 1970s, but a 2014 study analyzing the answers of more than 10,000 people in Japan and the United States found no meaningful link between blood type and personality (Nawata, 2014).

Saju was never built to be tested as a predictor of personality, and studies showing such evidence are hard to find. Its structure also gives everyone born on the same day in the same two-hour block the same eight characters, so saju alone struggles to explain why people born at the same time grow up with different personalities. That is why this site presents how to read saju as a cultural reading, not a measurement.

The rule of thumb is simple. If you want to change or decide something based on the result, use a test that measures your answers; if the goal is conversation and fun, pick whatever appeals to you. Here it is by situation.

When you want to know your tendencies accurately: start with the Big Five personality test. Each trait comes back as a score, so you see strengths and soft spots together (“extraversion middling, conscientiousness high”), and retaking it after a few months shows how you have changed.

When you want to talk about differences with friends or a team: the MBTI test is the easy choice. Four letters are easy to remember and already widely used, so conversations open quickly. If your result keeps changing between attempts, see how to read MBTI and the Big Five together.

When the question is specific, such as dating or career: a test built for that question beats a personality type. If you wonder about recurring anxiety or distance in relationships, try the attachment style test; if you wonder what kind of work interests you, try the RIASEC career interest test.

When you want to chat with friends or enjoy the New Year mood: zodiac signs, blood types and saju are perfect. If you are a Leo, read the sign profile and Leo compatibility with a friend, or share a laugh over blood type compatibility. Since it is for fun, you can shrug off any reading you do not like.

When choosing whom to hire or whom to date: do not use any of the five as the sole basis. Psychological tests are aids to self-understanding, not scores for selecting people, and screening people by information fixed at birth means judging them by something they cannot change.

If you have ever read a zodiac or blood type profile and thought “how is this so accurate?”, nothing strange is going on. In a classroom experiment published in 1949, the psychologist Bertram Forer handed his students what he said were individual personality sketches, which were in fact all the same text, and the students rated it as a very good fit for themselves (Forer, 1949). This tendency to accept broad statements that fit almost anyone as being about you is called the Barnum effect.

Sentences such as “cheerful on the outside but full of thoughts inside” or “warm with close friends but shy at first” apply to most people to some degree. Add confirmation bias, the habit of remembering moments that fit our beliefs and forgetting the ones that do not, and a description feels more and more accurate. An analysis of yearly Japanese survey data from 1978 to 1988 also reported that, as blood type talk spread, people’s self-descriptions drifted slightly toward the stereotype of their own type (Sakamoto & Yamazaki, 2004), which suggests belief can create some of the resemblance.

Psychological tests are not fully immune to this trap either. Feeling that a description fits and the test being accurate are different matters, which is why researchers judge evidence by retesting the same people and comparing results with real behavior rather than by impressions. Put the other way round, a feeling of fit alone cannot tell you which system is better. The same goes for left-brained and right-brained types, which sound like brain science: the two hemispheres do divide some of the work, but the studies in the left-brain/right-brain guide give no grounds for sorting people into two types.

Q. Which is the most accurate: MBTI, blood type, zodiac sign or saju? A. For measuring personality, the Big Five has the strongest evidence, MBTI comes next, and blood type, zodiac sign and saju have no evidence of predicting personality. Those three are closer to stories enjoyed as culture than to tools competing on accuracy.

Q. Isn’t MBTI just as unscientific as blood type? A. No: MBTI measures tendencies from your own answers, and research shows its scores connect meaningfully with Big Five traits. Its clear weakness is that cutting scores in two to assign types makes results prone to change.

Q. But my zodiac sign or blood type description fits me perfectly. A. Feeling that it fits is natural, but the feeling is not evidence. The Barnum effect (taking broad statements that fit anyone as personal) and confirmation bias (remembering only the moments that fit) work together.

Q. Do saju and zodiac signs work the same way? A. No: both are fixed by when you were born, but saju uses eight characters of the East Asian calendar while zodiac signs use the section of the ecliptic the Sun was in on your birthday. Saju also uses the date and hour, so it divides people far more finely, as the 60 day pillars show, but finer division does not create evidence.

Q. Should I stop reading them for fun? A. There is no need to stop. Enjoy them as conversation, and just do not use them to judge people or to make important decisions.

First, do not use them to judge people. Lines such as “you are selfish because you are Type B” or “I never get along with that sign” may start as jokes, but they land as labels. In Japan, pressuring people over their blood type became enough of a problem to earn its own name, “bura-hara” (blood type harassment).

Second, make important decisions with real information. Weighty choices such as changing jobs, marriage, investments or health belong to actual conditions, reliable information and, when needed, professional advice, not to saju or the stars. Psychological test results are not diagnoses either; if you keep struggling, look for support before looking at results.

Third, keep fun and self-understanding in separate places. Use zodiac signs, blood types and saju as stories that make conversation lively, and the Big Five and MBTI as mirrors for observing yourself, and the two never collide. Find your sign in the zodiac sign dates and laugh about it with a friend today, then take the Big Five test on a day you want to know yourself better.

References: McCrae & Costa (1989), Journal of Personality 57(1); Pittenger (2005), Consulting Psychology Journal: Practice and Research 57(3); Roberts, Kuncel, Shiner, Caspi & Goldberg (2007), Perspectives on Psychological Science 2(4); Soto (2019), Psychological Science 30(5); Carlson (1985), Nature 318; Hartmann, Reuter & Nyborg (2006), Personality and Individual Differences 40(7); Nawata (2014), Japanese Journal of Psychology 85(2); Sakamoto & Yamazaki (2004), Progress in Asian Social Psychology 4; Forer (1949), Journal of Abnormal and Social Psychology 44(1).