Conclusion

We demonstrated a clear relationship between blood type and the self-reported personality of many single question items, which matches traits previously stated. The effect of blood type on personality was shown as partial η2 = 0.053 at the maximum in this study ‒ the effect size was medium. The same traits were observed in the two no-knowledge groups, though the difference was smaller. People with no-knowledge of blood type traits might be less concerned or sensitive to personality. A person without blood type knowledge had lower scores of sociability and empathy, while those with more knowledge had higher. If no-knowledge group has low sensitivity of the personality, thereby the difference becomes small. This idea corresponds with the actual data.
Blood type does not uniquely affect a person’s personality. On the contrary, various factors such as gender and age have an intricate and significant impact. This makes it impossible to achieve consistent results without taking these non-linear interactions into account. Traditional personality tests, such as the Big Five test, typically use a personality factor that consists of multiple items. In this case, the effect of blood type fluctuates, which can produce inconsistent results unless the gender, age, or other conditions of the sample are properly controlled. The explanation above is in good agreement with the theory of personality psychology. Our findings provide a new, if hypothetical, framework of how genes affect human personality.
Meanwhile, the sample in this study was limited to Japanese populations only, the AI training data was small in sample size, its use was experimental, and the interaction between gender and age is still unknown. Additional research using larger, global dataset is needed in order to address true implications as well as to improve algorithms and methodologies.