Does blood type predict personality? What studies show

“Type A people are meticulous, Type B people are free spirits”: you have probably heard something like it. mind.io’s blood type personality pages also describe how Types A, B, O and AB are usually portrayed, but from the start they present this as popular culture, read for fun. So is there any scientific basis for a link between blood type and personality? This guide answers that question with research.

The short answer is that large surveys and studies with personality tests have mostly found no meaningful link between blood type and personality, and a study that did report a small difference was called preliminary by its own authors (Tsuchimine et al., 2015). In a reanalysis of surveys answered by more than 10,000 people in Japan and the United States, blood type explained at most 0.3% of the differences in answers (Nawata, 2014). Some research also finds that people who firmly believe in blood type personality tend to describe themselves in line with it, so there are reasons why it can feel accurate (Cho et al., 2005).

This guide covers how the idea began, what the large surveys and personality-test studies found, why it feels accurate, when a joke becomes a label, and how to enjoy it without taking it as fact. A side-by-side comparison with MBTI, zodiac signs and saju is in the guide comparing MBTI, blood type, zodiac signs and saju. mind.io does not offer a test that judges personality by blood type.

The study usually named as the starting point of blood type personality theory is “A study of temperament by means of human blood groups”, published in the Japanese Journal of Psychology in 1927 by the Japanese educator Takeji Furukawa. The paper shows that he first looked at 11 of his own relatives, then widened the circle to 50 staff, graduates and friends of the Tokyo Women’s Higher Normal School, and then to 269 students of that school and a teacher-training institute. Participants answered items on whether they were active or passive, or rated their classmates, and were blood-typed afterwards (Furukawa, 1927).

Furukawa concluded that blood type was the most important factor setting the basis of a person’s temperament. Yet he wrote at the start of the paper that, as a first attempt, it had many shortcomings, and he explained people whose temperament did not match their type by the gene combination their parents carried (Furukawa, 1927). If even the cases that do not fit can be explained away, a theory becomes hard to prove wrong whatever the results. His samples were also limited to people around him, and after many later attempts to check it, the theory was judged academically invalid (Nawata, 2014).

The idea returned to popular culture through books such as Masahiko Nomi’s 1971 “Compatibility you can tell by blood type” (Nawata, 2014). In 2004, 70 Japanese television programmes ran blood type personality specials (Uemura & Sato, 2006, cited in Nawata, 2014), and in 2008 all four books of a blood-type “self-manual” series made that year’s top 10 sellers (Nawata, 2014). A study that sorted the explanations aired during this period judged that none was logically valid, including those that borrowed recent science such as evolution or brain research (Uemura & Sato, 2006).

In Korea, too, blood type personality has long been a favourite topic of conversation. A 2005 paper in a Korean journal noted that the link between blood type and personality was drawing wide public interest and tested it directly (Cho et al., 2005). Its results come later in this guide.

A widely cited large-survey test of the idea is Kengo Nawata’s 2014 analysis in the Japanese Journal of Psychology. He reanalysed three sets of economics survey data collected by Osaka University. The Japanese surveys of 2004 (2,878 to 2,938 people, depending on the item) and 2005 (3,618 to 3,692) were random samples of adults aged 20 to 69 drawn from residents’ registers, and the US survey of 2004 (3,037 to 3,092) came from a research firm’s respondent panel, matched to the population’s make-up. People reported their own blood type (Nawata, 2014).

Across the three surveys, 68 items on attitudes to everyday life were compared by blood type, and 65 showed no significant difference. The 3 that did were about what chance alone would produce in 68 tests, an average of 3.4, and on the item “I worry about my children’s future”, Type AB scored highest in Japan but lowest in the US, so even the direction disagreed. The share explained by blood type (the effect size) was at most 0.3% for every item, and even on the item with the largest effect, the gap between blood types was 0.25 points on a 1-to-5 scale (Nawata, 2014).

Nawata named a limitation himself. The items were written for an economics survey, not as standardised personality-test items. Still, he argued that if blood type shaped personality, a sample this large would have shown differences in everyday attitudes too, and concluded that the results are evidence that blood type and personality are unrelated (Nawata, 2014).

The same paper also describes Yutaka Matsui’s 1991 analysis of four large Japanese surveys from 1980 to 1988 (12,418 people in all). Of 24 items, only 1 showed a difference between blood types in all four surveys, and even on that item the highest-scoring type changed from year to year (Matsui, 1991, cited in Nawata, 2014). If the top type changes every year, the difference is hard to put down to blood type.

To the objection that everyday-attitude items might simply miss the differences, studies with standard personality tests offer an answer. One recruited 360 blood donors and analysed 240 of them, 30 men and 30 women of each blood type. It predicted that Type B would score higher on neuroticism, Type O on extraversion and optimism, Type A on agreeableness and Type AB on conscientiousness, yet found no differences by blood type (Rogers & Glendon, 2003). A study that measured the Big Five in Canadian university students was also reported to have found no significant relationship with blood type (Cramer & Imaike, 2002, cited in Wu et al., 2005, and Nawata, 2014).

A study in which 2,681 Taiwanese high school students completed a Big Five test (the NEO-PI-R) likewise found no significant relationship between blood type and personality. The one exception was that Type AB girls scored lower on conscientiousness, and the researchers judged that this might be chance, since the group was small at 78 (Wu et al., 2005). That is the opposite of the earlier study’s prediction that Type AB would score higher on conscientiousness.

Research from Korea points the same way. In a survey of 204 university students, Big Five scores showed no meaningful relationship with blood type (Cho et al., 2005). Another study in a Korean journal asked 496 people about their love styles and their attitudes as partners and found no meaningful differences by blood type; the authors concluded that explaining compatibility or dating styles by blood type was not supported. They added that gender and dating experience might change the gaps between blood types on some measures, and the study did not compare couples’ blood type pairings directly (Joo & Park, 2006).

One study did report a small difference. Researchers confirmed the blood types of 1,427 Japanese medical students and medical staff by genotyping and compared the seven scales of a temperament and character test (the TCI). Only on one scale, persistence, the tendency to keep going despite frustration and fatigue, did Type A score slightly higher than Types B and O. The share explained by blood type was small, 0.6% (1.0% when grouped by genotype), and the researchers wrote that the result should be regarded as preliminary and interpreted with caution, and that their sample might not represent the general population (Tsuchimine et al., 2015). A small difference on one scale is a long way from proving that “Type A people are meticulous”.

The Korean study of 204 university students had one more interesting result. When personality was measured not with the Big Five but with the adjectives usually attached to each blood type (for Type A, “timid”, for example), differences between blood types did appear, especially for Types A and B, whose stereotypes are the clearest. But the pattern came from people who firmly believed in blood type personality; among those who did not, there was no difference by blood type even on the stereotype adjectives. The researchers interpreted this as suggesting that belief can change how people rate themselves and others even where no real link exists (Cho et al., 2005).

Studies from Japan point the same way. According to Nawata’s review, there are studies in which several items showed blood type differences in how people saw their own personality among believers, but almost none among non-believers (Nawata, 2014). An analysis of yearly Japanese surveys from 1978 to 1988 reported that during the 1980s, as blood type talk spread, the answers of Type A people shifted toward the Type A stereotype (Sakamoto & Yamazaki, 2004, cited in Nawata, 2014). In data from the 2000s, however, no differences between blood types appeared, and Nawata concluded that a self-fulfilling prophecy, with belief hardening into real differences, had not taken place (Nawata, 2014).

Two familiar habits of mind add to this. One is the Barnum effect, taking a vague description that fits almost anyone as being about you. 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 the sketch as a good fit for themselves (Forer, 1949). The other is confirmation bias, remembering the moments that fit what we expect and letting the others slip by. “Typical Type A, so meticulous” sticks in memory, while the scatterbrained Type A friend is quickly forgotten.

In short, blood type personality probably feels accurate less because blood type shapes personality than because the descriptions are broad and we see ourselves and others through them. And just as Furukawa explained away the cases that did not fit by the parents’ genes (Furukawa, 1927), the habit of writing off exceptions keeps the belief alive.

Blood type talk does not always stay light. On 8 December 2004 the youth committee of Japan’s Broadcasting Ethics & Program Improvement Organization (BPO) said that blood type programmes were treating the link between blood type and personality as if it had been proven, and asked broadcasters not to encourage the view that blood type determines a person’s character. The committee wrote that sorting and valuing people by a blood type they cannot change risks leading to social discrimination, and that children, whose judgement is still developing, might come to hold the stereotype that blood type fixes personality (BPO, 2004).

Among the viewers’ comments quoted in the same document was the complaint that blood type discrimination was emerging at school and in job hunting. Broadcasters had started adding captions such as “there are individual differences”, but the committee considered these no more than excuses (BPO, 2004). The document was a request from a broadcasting ethics body, not a legal ban, but it pointed out that sorting begun for fun can turn into a yardstick for judging people.

So remarks like “you are selfish because you are Type B” or “I never get along with Type AB” can land as labels, even as jokes. Nobody chooses their blood type, and as the studies above show, it does not reveal personality. Where people’s chances are decided, such as hiring, promotion or putting together a team, blood type should be neither asked about nor taken into account.

Blood type talk is a handy conversation starter with someone new, or a way to tease friends and laugh together. What the research shows is that blood type cannot tell you someone’s personality, not that you should never talk about it. A few habits make it much easier to enjoy.

First, read the other types’ descriptions too. Put the Type A, Type B, Type O and Type AB descriptions side by side, and you will probably find quite a few lines that make you nod even though they are not about your type. It is the easiest way to see the Barnum effect for yourself.

Second, turn the descriptions into questions. Instead of “You are Type O, so you are easy-going, right?”, ask “How are you when something big is coming up?”, and the same topic helps you actually get to know the person. Third, laugh off the descriptions that do not fit, and never use them to pick or rule out people. Blood type compatibility is most fun read as a way to learn about each other.

Fourth, on days when you want to know yourself better, try a test that measures your current tendencies from your answers. The Big Five personality test measures five traits widely used in personality research, and the MBTI test shows a type built from four preferences. Unlike blood type, both give results from the items you answer, and the results can change when you change. How far you can trust the MBTI is covered in the guide to MBTI accuracy. A test result does not mean it is linked to your blood type.

Q. Is there any scientific evidence for blood type personality? A. Going by the research so far, the fair answer is no. In surveys answered by more than 10,000 people in Japan and the US, blood type explained at most 0.3% (Nawata, 2014), and studies using standard personality tests with blood donors, Taiwanese high school students and Korean university students found no meaningful link either (Rogers & Glendon, 2003; Wu et al., 2005; Cho et al., 2005). One study did report a small difference, but its authors called the result preliminary (Tsuchimine et al., 2015).

Q. But my blood type description fits me perfectly. A. Feeling that way is natural. People who firmly believed in blood type personality tended to describe themselves in line with the stereotype, while no such difference appeared among those who did not (Cho et al., 2005). The Barnum effect, taking a description that fits almost anyone as being about you, plays a part too. Read the other types’ descriptions and you will likely find that those lines fit you quite well as well.

Q. Are Type A people really meticulous and diligent? A. That is hard to support. In the study of Japanese medical students and staff, Type A scored slightly higher on persistence, but blood type explained 0.6%, and the researchers themselves called the result preliminary (Tsuchimine et al., 2015). In the Taiwanese high school study, the only difference in conscientiousness was that Type AB girls scored lower, which the researchers thought might be chance (Wu et al., 2005). That blood type explained at most 0.3% of the differences in answers also means that the differences between people of the same blood type are far larger (Nawata, 2014).

Q. Is blood type compatibility reliable? A. We found no study that tested it directly and supported it. In a study in a Korean journal, the love styles and partner attitudes of 496 people did not differ meaningfully by blood type, and the authors concluded that explaining compatibility or dating styles by blood type was not supported (Joo & Park, 2006). The study did not compare couples’ blood type pairings directly, so enjoy compatibility charts as a way to get to know each other.

Q. Isn’t the MBTI just the same thing as blood type? A. No. Blood type is fixed at birth and stays the same for life, while the MBTI measures your current preferences from the items you answer. The MBTI does have a limit, though: it sorts scores into two halves to assign a type, so results can change when you retake it. A fuller comparison is in the guide comparing MBTI, blood type, zodiac signs and saju and the guide to MBTI accuracy.

Q. Is there a blood type personality test? A. mind.io does not offer a test that judges personality by blood type. The blood type personality pages are a reading, for fun, of how the four types are usually portrayed. If you want to look at your tendencies through your own answers, try the Big Five personality test. Its result is not linked to your blood type.

References: Nawata, K. (2014), No relationship between blood type and personality: evidence from large-scale surveys in Japan and the US [in Japanese], The Japanese Journal of Psychology 85(2), 148-156, https://doi.org/10.4992/jjpsy.85.13016; Furukawa, T. (1927), A study of temperament by means of human blood groups [in Japanese], The Japanese Journal of Psychology 2(4), 612-634, https://doi.org/10.4992/jjpsy.2.612; Uemura, A., & Sato, T. (2006), Blood-typing as a pseudo-personality theory and diversity of its explanatory styles [in Japanese], The Japanese Journal of Personality 15(1), 33-47, https://doi.org/10.2132/personality.15.33; Matsui, Y. (1991), A statistical examination of personality differences by blood type [in Japanese], Bulletin of Tokyo Metropolitan Tachikawa College 24, 51-54 (cited in Nawata, 2014); Rogers, M., & Glendon, A. I. (2003), Blood type and personality, Personality and Individual Differences 34(7), 1099-1112, https://doi.org/10.1016/S0191-8869(02)00101-0; Cramer, K. M., & Imaike, E. (2002), Personality, blood type, and the five-factor model, Personality and Individual Differences 32(4), 621-626, https://doi.org/10.1016/S0191-8869(01)00064-2 (cited in Wu et al., 2005, and Nawata, 2014); Wu, K., Lindsted, K. D., & Lee, J. W. (2005), Blood type and the five factors of personality in Asia, Personality and Individual Differences 38(4), 797-808, https://doi.org/10.1016/j.paid.2004.06.004; Cho, S., Suh, E. M., & Noh, Y. (2005), Beliefs about blood types and traits and their reflections in self-reported personality [in Korean], Korean Journal of Social and Personality Psychology 19(4), 33-47, https://accesson.kr/ksppa/v.19/4/33/14576; Joo, H., & Park, S. (2006), Can blood type determine love? Love styles and love attitudes by blood type [in Korean], Korean Journal of Social and Personality Psychology 20(3), 67-80, https://accesson.kr/ksppa/v.20/3/67/14588; Tsuchimine, S., Saruwatari, J., Kaneda, A., & Yasui-Furukori, N. (2015), ABO blood type and personality traits in healthy Japanese subjects, PLoS ONE 10(5), e0126983, https://doi.org/10.1371/journal.pone.0126983; Sakamoto, A., & Yamazaki, K. (2004), Blood-typical personality stereotypes and self-fulfilling prophecy: a natural experiment with time-series data of 1978-1988, in Y. Kashima et al. (Eds.), Progress in Asian Social Psychology 4, 239-262 (cited in Nawata, 2014); Forer, B. R. (1949), The fallacy of personal validation: a classroom demonstration of gullibility, Journal of Abnormal and Social Psychology 44(1), 118-123, https://doi.org/10.1037/h0059240; Broadcasting Ethics & Program Improvement Organization, Youth Programming Committee (2004), Request concerning programmes that deal with blood types [in Japanese], 8 December 2004, https://www.bpo.gr.jp/?p=5125