Despite the widespread popular belief in Japan about a relationship between personality and ABO blood type, this association has not been empirically substantiated. This study provides more robust evidence that there is no relationship between blood type and personality, through a secondary analysis of large-scale survey data. Recent data (after 2000) were collected using large-scale random sampling from over 10,000 people in total from both Japan and the US. Effect sizes were calculated. Japanese datasets from 2004 (N = 2,878-2,938), and 2,005 (N = 3,618-3,692) as well as one dataset from the US in 2004 (N= 3,037-3,092) were used. In all the datasets, 65 of 68 items yielded non-significant differences between blood groups. Effect sizes (η2) were less than .003. This means that blood type explained less than 0.3% of the total variance in personality. These results show the non-relevance of blood type for personality.
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