Introduction
Background
Currently, the effect of genetic factors on personality is estimated to
be approximately 50% (Ando et al. 2004; Gerra et al., 2000, Keller et
al., 2005). The ABO blood group, discovered by Karl Landsteiner in 1901,
is a genetically determined and easily measured biological marker.
Hence, much research has been conducted not only on health risks, but
also on its impact on personality.
The relationship between blood type and personality is studied at an
international scale, and the first academic one using statistics a base
was conducted in 1927, by Takeji Furukawa, a Japanese educational
psychologist (Furukawa, 1927 & 1930; Nawata, 2014; Rogers et al., 2003;
Sato et al., 1992; Wu et al., 2005). Yet, the epoch that most shape
present-day research is a Japanese book (Nomi, 1971) written by Masahiko
Nomi, a Japanese independent researcher, as well as an English book
(Nomi et al., 1988) written by his son, Toshitaka Nomi, and Alexander
Besher (Nawata, 2014; Rogers et al., 2003; Sato et al., 1992).
Results of Recent Academic
Studies
Questionnaire-based personality assessment, frequently used in
psychology and consists of answering to multiple questions regarding
multiple self-reported personality traits and integrating into several
personality factors by statistical processing. In theory, this means
that the self-reported answer will either directly or indirectly appear
in the result. Although there are many academic studies on the
relationship between blood type and personality, the inconsistency among
results (Cattell et al., 1964; Cho et al., 2005; Cramer et al., 2002;
Flegr et al., 2013; Furukawa, 1927 & 1930; Gupta, 1990; Jogawar, 1983;
Kim et al., 2007; Lester et al., 1987; Mao et al., 1991; Nawata, 2014;
Rogers et al., 2003; Sharifi et al., 2015; Sato et al., 1992; Shimizu et
al., 2011; Wu et al., 2005) has led to the endless academic controversy
about whether the relationship is scientifically confirmed. Many studies
examined the association between blood type and personality using the
“Big Five” personality test (Goldberg, 1990 & 1992), which has been
extensively present in contemporary psychology. However, none of these
results was certified as consistent (Cho et al., 2005; Cramer et al.,
2002; Flegr, et al., 2013; Rogers et al., 2003; Sharifi et al., 2015;
Shimizu et al., 2011; Wu et al., 2005). In 2014, a study that analyzed
data of large-scale social surveys in Japan and the US was conducted,
yet the study over 10,000 participants revealed no meaningful difference
(Nawata, 2014).
Self-fulfilling
Prophecy
Self-fulfilling prophecy refers to the phenomenon in which a person who
believes in a prophecy learns to act in accordance with the prophecy,
thereby bringing the prophecy to being. An example that psychologists
have studied is astrology (Glick et al., 1986; Eysenck et al., 1982;
Snyder, 1984). If a person’s original personality and his/her sign
matches, that tendency becomes stronger. Even if the personality and the
sign do not initially match, the personality moves toward what has been
indicated. In Japan, South Korea, and Taiwan, roughly half of the people
feel the relationship between blood type and personality is
legitimate (Cho et al., 2005;
Kamise et al., 1994 & 1995; Sato et al., 1992; Wu et al., 2005;
Yamaoka, 2009). Logically, the self-fulfilling findings among astrology
suggest that one’s personality would change in a direction that fits
relevant as personality description – of which shown by blood type.
Based on this self-fulfilling prophecy hypothesis, several large-scale
surveys in Japan which were designed or analyzed by psychologists or
other academic researchers after 1990, clearly confirmed the phenomenon
(Matsui, 1991; Muto et al., 2012; Ryu et al., 2007; Sakamoto et al.,
2004; Yamaoka, 2009; Yamazaki et al., 1991). Archetypical sample sizes
of these were 6,660 (Yamaoka, 2009), 11,766 (Matsui, 1991), 32,347
(Sakamoto et al., 2004; Yamazaki et al., 1991 – these two used the same
sample) and over 100,000 (Muto et al., 2012; our estimation; the exact
number was not specified in this report, although it alluded the size
was much larger than preceding ones). Nevertheless, there is not
existing coherent statistical difference in respondents without
knowledge of astrology or blood type. The current scientific consensus
is that these differences are self-fulfilling phenomena induced by the
“contamination by knowledge” (Cramer et al., 2002; Eysenck, 1982; Kim
et al., 2007; Matsui, 1991; Ryu et al., 2007; Sakamoto et al., 2004;
Sato et al., 1992; Yamaoka, 2009; Yamazaki et al., 1991).
Contemporary Trends and
Issues
After 2000, a growing number of studies proved the previously questioned
link between blood type and physical constitution, with the exception
being in the weak gastrointestinal tract: this demonstration proposed a
new approach to medicine (Ewald et al., 2016; Risch, 2000). There had
also been several studies on biological factors, which investigated
whether physical constitution affected personality (Hobgood, 2011a &
2011b). In 2015, a genotype of blood type and the TCI Personality Test
had been determined to be related, as predicted by blood type
personality theory (Tsuchimine et al., 2015).
It is understood that personality involves complex interactions of
genetic factors such as gender and age, and such interactions between
these factors are typically non-linear (Kawamoto et al., 2015; Lehmann
et al., 2013; Weisberg et al., 2011). However, the majority of the
previous studies assumed that the effect of blood type is linear and
coherent, regardless of gender or age (Cattell et al., 1964; Cho et al.,
2005; Cramer et al., 2002; Flegr et al., 2013; Furukawa, 1927 & 1930;
Gupta, 1990; Jogawar, 1983; Kim et al., 2007; Lester et al., 1987;
Nawata, 2014; Rogers et al., 2003; Sharifi et al., 2015; Sato et al.,
1992; Shimizu et al., 2011; Wu et al., 2005). Statistical methods used
to design questionnaire-based personality tests, such as principal
component analysis and correlation analysis, basically assume a linear
relationship between variables. Therefore, there is no theoretical
guarantee that these statistical methods or personality tests will
accurately analyze real, non-linear data.