Matchmaking groups in Japan use blood typing as a criterion and there are actually speed dating groups set up so people can meet people with a certain blood type.
According to the BBC report, many Japanese believe that people with type A are "dependable, self sacrificing, but also reserved and prone to worry." People with type O are decisive and confident.
A recent study compared 589 ABO compatible (that is, the husband and wife had blood types which could be exchanged) against 432 ABO incompatible mating couples.
The mean number of living children presents a significant difference.
This is not true in blacks, where the anti-B levels are almost as high as were the levels of anti-A in both men and women.