Methods
Participants
The data used in this study (Supplementary Material File) was collected
by the means of crowdsourcing throughout Japan. All samples were
allocated by gender, as well as 10-year increments of age. With the
intention of avoiding ethical issues, question items on blood type
characteristics of this study (Table 5 and Appendix A) were extracted
from reviewed academic articles (Sato et al., 1991; Watanabe 1994;
Yamazaki & Sakamoto, 1991& 1992 – Tables 2-4). These items were
checked again at the previously stated crowdsourcing company which has
been passed the Japanese privacy mark (JIS Q 15001). The company
confirmed that there was no problem with the question items. It provides
customers with anonymized data and obtains informed consent from
participants (respondents) prior to its surveys.
Instruments
Survey 1 was conducted in 2018 as a preliminary study with a sample size
of 1,000. Japanese single individuals with the age of 20-39 were asked
to rate a total of 8 items representing 4 blood type (A, B, O, AB)
characteristics, each with scores of 1-5 for their personality traits
(the larger the number, the more fitting the trait), and scores of 1 to
4 of relationship and their knowledge on the level between blood type
and personality (the larger the number, the more related or informed).
Survey 2 was conducted in 2019, and covered 2,000 Japanese people ages
20-59, further expanded blood type characteristics to 12 items, and
asked the respondents to answer which blood type they thought these 12
items would categorize. In Survey 2, we added an item of marital status,
since the age of participants spanned to 59, which meant that married
persons were included.
Each participant’s blood type of was determined by self-report, because
most Japanese people know their blood
type.
In Japan, many people know their
blood type because, until recently, it had been common practice to test
the blood type of newborns. In Survey 1, the dataset included only those
who knew their blood type, as previously instructed. Hence, the valid
sample size was 1,000. In Survey 2, 141 out of all the 2,000
respondents, or 7.1% of the total, did not know their blood type.
Thereby the data of the remaining 1,859 participants with known blood
types were used. The distributions of blood types were almost equal to
the Japanese average measured by the Japan Red Cross Blood Center; A:
39.1%, B: 21.5%, O: 29.4%, AB: 10.0% (Okubo, 1997).