Jisu Yoon, freshman in aerospace engineering, laughed as his friend, Jessica Lim, sophomore in chemistry, called him “psycho.”

However, that’s what Yoon’s blood type predicts.

In astrology, horoscopes reveal an individual’s personality based on his or her birthday, but in Korea and Japan, people’s horoscopes are determined by blood type.

The whole idea began in the 1930s, when a Japanese researcher named Furukawa Takeji suggested there is a link between a person’s blood type and his or her personality.

Yoon, whose blood type is AB, said he agrees with his friends about his personality. “I am also a genius,” he added.

Lim explained: “It means either you are very smart or crazy, because ABs think very differently.”

Both Yoon and Lim said knowing your blood type is very common in Korean culture.

As with any tool that generalizes personality, stereotypes can be created.

“In Korea, it is not good for a male to be B,” Lim said. “It means they have good looks and a good appearance, but they are not the same inside.”

In 2005, the romantic comedy “My Boyfriend is Type B,” was released in South Korea. The movie was about a Korean man and woman who find interest in each other, although their blood types say they are incompatible.

The blood type A can also correspond with unflattering personality traits.

“If the person is too narrow-minded, we call them triple A,” Lim said.

Lim said that often people are nothing like their blood type descriptions, and it’s just for fun.

“In my church in Ames, one day the Korean students started talking about each other’s blood types,” she said. “We use it as a tool to begin a conversation or get closer to people by finding common characteristics.”

Yoon’s roommate, Norikazu Soga, graduate student in animal science from Japan, has blood type B.

Soga said knowing one’s blood type is common in Japan.

“It is especially common among girls,” Soga said. “When I go out with Japanese girls, they almost always ask me my blood type.”

Takeji said not only does blood type define personality, but it also predicts compatibility. For example, Lim has blood type O and her boyfriend has blood type A.

“For blood type O girl, a blood type A guy is most compatible, and B is least compatible,” Lim said. “In Korea, I find a lot of guys who have blood type O and A, but here there are many more AB and B types.”