The relation between ABO blood types and personality was studied and brought to life by Mashiko Nomi, a Japanese journalist, in the 1970s. Nomi's interest was sparked by a paper titled The Study of Temperament Through Blood Type, published by Takeji Furukawa in 1927, in the journal Psychological Research. Although lacking a strong scientific explanation, and being dismissed by members of the scientific community, popular belief subscribes most wholeheartedly to this concept.
Various personality traits associated with the four different blood types under the ABO system, have been provided below.
Today, the relation between blood type and personality is followed closely in Japan, much like the use of sun signs to determine personality and compatibility for matchmaking.