A Probabilistic Solution for the Mystery of Japanese Blood Type Prediction
Accuracy
Hideo Hirose, Kyushu Institute of Technology, Japan
Asian Conference on Psychology & the Behavioral Sciences 2015
Official Conference Proceedings
Abstract
In Japan, a belief that there is a relationship between personality and ABO bloodtypes seems to have subsided now. Statistical hypothesis test results deny that
relationship for many times up to now. However, many people still like to talk about
blood types in connection with personality. They believe in predicting the blood typeof one person with accuracy over a probability of 0.25 which is the mean value inproviding the correct answer under the condition that they select one of the blood
types at random. Actually, the questionnaire results we took several times reveal us anintriguing phenomenon; in Japan, blood type A and O were more accurately predicted
than the random selection probability of 0.25. In the questionnaires, personality
questions were not included, and this approach is new. In this research, we focused on
the human intuition ability in predicting the blood types. That is, we investigatedwhether the correct answer ratio of human intuition is superior to the probability ofrandom selection. Based on the conditional probability and Bayes theories, we showthat this kind of superficial result can be expected as a natural phenomenon. We haverevealed that people implicitly use the underlying knowledge of relationship between
personality and ABO blood types as imprinting, which shows us superficial humanintuition ability.
Keywords: blood type, personality, new questionnaire, human intuition, Bayes
theory, imprinting

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Introduction
In Japan, a belief that there is a relationship between personality and ABO bloodtypes seems to have subsided now. Statistical hypothesis test results deny that
relationship for many times up to now. A recent statistical research result also showsthat such a relationship does not exist (Rogers & Glendon (2003), and Nawata,(2014)). Another approach rejecting the relationship by using the machine learning isseen in Hirose & Yukizane (2008), which is shown in appendix. However, many
people still like to talk about blood types of persons. They may be interested inknowing personality of someone by an indirect method actually, and this underlying
hidden information could be blood type. That is, implicitly, we are inclined to connect
the blood types and personality.
On the other hand, many persons guess someone’s blood type without knowing
his/her personality. They believe in predicting the blood type of one person withaccuracy over a probability of 0.25 which is the mean value in providing the correct
answer under the condition that they select one of the blood types at random. It is very
intriguing that blood type discussions in many cases are performed without
personality. How can they guess other’s blood types? This naïve question is one of themotivations of this paper.
Questionnaire 1
We first performed a new questionnaire in our research laboratory (B4, masterstudents, and doctor students) because they know others to each other. The question is
only one: “Guess someone’s blood type.” Figure 1 is a result of that. In the figure,row means the person who guesses someone’s blood type, and column means theperson whose blood type is estimated. Using successful and unsuccessful number ofpersons in estimation, a hypothesis test result is shown in Figure 2, where therandomness is not rejected. However, the number of samples was rather small.

Figure 1: A result of questionnaire 1.

Figure 2: Hypothesis test to the result of questionnaire 1.
Then, we made the same questionnaire to a larger group, a class consisting of 80
sophomore students. Figure 3 shows the result of it. It is interesting that this time thecorrectly estimated ratio becomes around 0.3 in total, and this is included in therejection region.

Figure 3: Hypothesis test 2 to another result of questionnaire 1.
Figure 3 may be rearranged by a matrix form as shown in Figure 4, where areas
indicate the difference among the blood types. It is clear that type A is dominantly
occupied and that type AB is a minority group.

Figure 4: Matrix form of another result of questionnaire 1.
Using Bayes theorem, we can induce the estimation ratios as shown in Figure 5.
These values are similar to the ratios computed from the observed values. From theBayes perspective, we can estimated the blood types with accuracy about 40% forblood type A, about 20-30% for blood type B and O, and about 10% for blood typeAB, when we used the observed values as prevalence values.

Figure 5: Bayes result to another result of questionnaire 1 (using observed ratios).

When we use the well-known common values as the prevalence values, we can derive
the commonly used ratios as shown in Figure 6. That is, we can estimated the bloodtypes with accuracy about 40% for blood type A, about 20% for blood type B, about
30% for blood type O, and about 10% for blood type AB. This means that the highaccuracy in estimating blood type A seems to be merely a superficial phenomenon.
We did not have high intuition abilities we might believe in. It can be explained justusing the randomness. However, how can they know the prevalence values for A, B,O, and AB blood types? We consider next this naïve question.

Figure 6: Bayes result to another result of questionnaire 1 (using prevalence ratios).
Questionnaire 2
Do we know the prevalence values for A, B, O, and AB blood types? If so, how can
we know them? Then, we made a next questionnaire: “How many persons are there
having characters in 10 persons shown below?” In many books explaining therelationship between blood types and personality, we can find typical connection
example as shown in Table 1. This may be originated somewhere in the literature(e.g., Sakamoto, A., & Yamazaki, K. (2004)), and this information is commonlyrecognized in Japan.

Table 1: Commonly recognized personality in blood types A, B, O, and AB.

We may assume that the ratio of some blood type in total is due to the prevalence
ratio of some characters in personality. For example, if we ask someone how many
persons there are in 10 persons having characters, “scrupulous, steady, or anxiousmind”. Then, he/she considers the percentage of persons having such characters. Thecharacters above could be majority of Japanese persons because such characters arecommonly seen in Japan. Actually, as Figure 7 shows the distribution to that question,
they think there are many persons having such characters. The mean value is 3.2, and50 percentile point is 3.1. More than three in ten persons are having such characters.

Figure 7: Result for the questionnaire: how many persons are there in 10 persons
having characters, “scrupulous, steady, or anxious mind?”Figures 8, 9 and 10 show the similar results for characters, “optimistic, own pace,freewheeling”, “broad-minded, sociable, unyielding”, and “unique, genius, dualpersonality”. The order of the ratios in ten persons to the questionnaire results reveals
that the result in Figure 7 is the first, that in Figure 9 is the next, those in Figure 8 and
10 follow in succession. This order is consistent to the order of the blood type ratios:
the first is A, next O, then B, and last AB.

The well-known prevalence ratios of Japanese blood types are 0.4 for type A, 0.2 fortype B, 0.3 for type O, and 0.1 for type AB. The blood type AB is regarded as aminority group.

Figure 8: Result for the questionnaire: how many persons are there in 10 persons
having characters, “optimistic, own pace, freewheeling?”

Figure 9: Result for the questionnaire: how many persons are there in 10 persons
having characters, “broad-minded, sociable, unyielding?”

Figure 10: Result for the questionnaire: how many persons are there in 10 persons
having characters, “unique, genius, dual personality?”
Figure 11 shows the box plot corresponding to Figures 7, 8, 9, and 10 although sometransformation is performed. That is, for one person, total ratio summing up from four
ratios to each blood type becomes one. In the figure, we can see some relationshipbetween the blood types and the guessing numbers of persons having somepersonalities. Figure 12 shows the correlation between the ratios of actual prevalence
one and those of the questionnaire results in mean values shown in Figure 11. The
correlation coefficient value is 0.92. In anyway, the guessing numbers of persons
having some personalities are consistent with the actual prevalence ratios of blood
types.

Figure 11: Correlation between the ratios of actual prevalence one and those of thequestionnaire results shown in Figure 7, 8, 9, and 10.

Figure 12: Correlation between the number of the actual prevalence and that of thequestionnaire results in mean values shown in Figure 11.
Therefore, we could construct a hypothesis that many people guess someone’s blood
type via the hidden personalities. One can estimate the percentages of typical humancharacters, and these percentages happen to coincide with those of blood types.
However, we cannot simply assume that there is a relationship between humancharacters and the blood types. Still, we can explain the accuracy of the estimatedvalues even if people do not know the blood types prevalence. Without knowing theactual prevalence ratios of blood types, we can guess someone’s blood type by withthe aid of personality ratios commonly pervaded. This is why we can guess others’
blood types more accurately (e.g., 0.3) than randomly estimated value (i.e., 0.25).
Discussion
Many researchers investigate the relationship between blood types and personality byusing questionnaires in which blood types and personality are included altogether.
This paper does not deal with the information of personality in questionnaires
directly; it deals with only the blood type questionnaire: one can estimate someone’s
blood type. This is a novel point of the paper. If no information about personality isprovided, the expected accuracy to correct answers seems to be 0.25 by randomness.
However, a higher accuracy, e.g., 0.3, is obtained by our questionnaires. It seems thatpeople first guess others’ personality, and then they connect blood types andpersonality with their own information, and finally they guess blood types. If this istrue, we have to assume that there may be some information about the relationshipbetween the blood types and personality. Where do they get such the information?
Are they medical or psychological references? We think that a source of theinformation could be imprinting developed over a long period of time through theliterature. However, we know such the information is unreliable nowadays.
The accuracy to correct answers obtained by our questionnaire seems to be one that
we know the prevalence ratios of blood types to the total. Therefore, we next tried tofind the prevalence ratios. To find the hidden information between blood types andpersonality, we performed a different questionnaire: how many persons there arehaving such and such personality in ten persons.

If the ratios of personality people replied are consistent with the actual prevalence
ratios, then we can estimate the blood types with a higher accuracy without theknowledge of the relationship between the blood types and personality. Only theratios have critical importance. No meaning in the knowledge. This is our conjecture.
Conclusion
In Japan, a belief that there is a relationship between personality and ABO bloodtypes seems to have subsided now, and statistical hypothesis test results deny that
relationship for many times up to now. However, many people still like to talk about
blood types in connection with personality. In the questionnaires, blood types andpersonality were included altogether. However, in this paper, personality questions
were not included, and this approach is new. In this research, we focused on thehuman intuition ability in predicting the blood types. That is, we investigated whether
the correct answer ratio of human intuition is superior to the probability of random
selection. Based on the conditional probability and Bayes theories, we show that thiskind of superficial result can be expected as a natural phenomenon. We have revealed
that people implicitly use the underlying knowledge of relationship between
personality and ABO blood types as imprinting, which shows us superficial humanintuition ability. A subsequent questionnaire regarding the prevalence ratios of somepersonalities assisted the conjecture that only the prevalence ratios make sense but therelationship knowledge between the blood types and personality.
Appendix
As commonly used questionnaires, we also obtained two sets of database for therelationship between the blood types and personalities of as shown in Figure 13. One
set is for sophomore class of fiscal year 2005, and the other is of 2006. A commonlyused method in classification is the decision tree as shown in the figure.

Figure 13: Questionnaire database and classification by using the tree.
We can construct the tree model by using the data set of 2005 and apply the model tothe same data set, as shown in Figure 14. In such an application, about 60% accuracy
for correct answers is obtained.

However, if we apply the model to the 2006 data set, the accuracy drastically reduced
to 40%, which is commonly seen in other cases. This accuracy is also obtained if all
the final leaves show the same class: blood type A is always estimated because A is
the most major group. The decision tree automatically constructs such the model, andactually it does not work at all.

Figure 14: Superficial and actual classification accuracies.

Figure 15: Japanese blood type prevalence ratios and the decision tree classification.

If we are in English-speaking world, the blood type prevalence ratios are seen in
Figure 16. Then, we will no longer be able to estimate the blood types by using thesame questionnaire 2 results.

Figure 16: Blood type prevalence ratios in English-speaking world.

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Contact email: hirose@ces.kyutech.ac.jp