What Has Been Found by Studies on Birth Order?


Quick Answer

Two research studies published in 2015 indicate that birth order has little to no effect on personality and only minimal impact on intelligence. Studies published in 2007 and 2003 came to the same conclusion.

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Although the debate about birth order figured significantly between Sigmund Freud and his co-worker Alfred Adler, and theories about birth order gained traction over the years, there is no scientifically viable study that confirms the order of a person's birth makes any notable impact on her emotional stability, extroversion, agreeableness, imagination or conscientiousness. While there may be an impact on intelligence, with firstborns ranking higher on IQ tests than later-born children, the impact was a mere one point.

Researchers from the Journal of Research in Personality studied 377,000 American high school students to test theories correlating personality and intelligence with birth order. They found a very slight discernible difference in personality based on the order of a person's birth. Scientists noted that firstborns may be more dominant and conscientiousness, which fits the long-standing stereotype, but contrary to the commonly held idea, firstborns also demonstrated a slightly more agreeable personality and were less neurotic.

After studying approximately 250,000 Norwegian conscripts in 2007 and accounting for family size, epidemiologists Petter Kristensen and Tor Bjerkedal concluded that the more older siblings a person has, the lower his IQ. However, the results were scant.

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