Frank J. Sulloway,  scholar  and  author of
“Born to Rebel,” a book on the significance of birth order, says oldest children are usually responsible. Firstborns are more likely to serve as (second) parents. They tend to be more conscientious, rule-keepers who also are ambitious and self-disciplined and dependable.
   Middle kids usually are peacekeepers who are social and diplomatic, according to Sulloway.
The little ones might argue occasionally, but lastborn children tend to be the most agreeable, humorous, fun-loving and amusing, more creative, outgoing and open to new experiences. They question authority and usually are leaders in social movements.
Kids without siblings often have traits similar to first-born kids. Only children, usually ambitious and good at following parents’ rules, are quite comfortable around adults, Sulloway adds.
學者作家蘇洛威在他有關出生排行重要性的著作《天生反骨》中提到，老大通常都有責任感。排行第一的小孩很可能被當作（第二個）父母，他們比較誠實謹慎、守規矩、也有企圖心、自律、可靠。
根據蘇洛威的研究，排行中間的孩子通常是和事佬，喜歡交際、處世圓融。
老么也許偶爾會爭吵，但通常最討人喜歡，幽默風趣又搞笑，比較有創造力、外向、開放心胸接受新經驗。他們會質疑權威，往往成為社會運動的領導者。
蘇洛威補充說，沒有兄弟姐妹的小孩通常有類似老大的特性，獨生子／女通常有企圖心、遵守父母的規定、與大人相處很輕鬆自在。