Research Question: t on personality? Birth-order could be one way to gain an understanding of friends, family members and co-workers. Research has shown that the birth-order indeed has an effect on personality. Birth-order of course does not explain everything about human behavior, personality is also affected by many different factors such as heritage, the environment of the upbringing, family size, education etc. There are four basic classifications of birth-order: the oldest, the only, the middle and the youngest born. Each has its own set ....