In this portrait of the Pailleron siblings, do you think Marie-Louise is fated to be spoiled while her older brother Édouard is sure to be bossy? “Portrait of Édouard and Marie-Louise Pailleron” by John Singer Sargent Licensed under Public Domain via Wikimedia Commons.

If you have siblings you’ve probably been told at one point or another that firstborns are bossy, the youngest is spoiled and the poor middle child is always neglected. People have been trying to figure out the effect of birth order on personality for over a hundred years and at times it feels that with each month a new study pops up either supporting or denying such an effect. The most recent paper to take a stab at this dispute used previously collected data from almost 20,000 American, British and German individuals. While the researchers from the University of Leipzig in Germany confirmed previous data that shows a slight decline in IQ from oldest to youngest, they found that birth order has no effect on personality.

The researchers analyzed the data from various angles, looking at the data both between families and within families, but their conclusions on the effect of birth order on personality were always the same: there was none. However, Dr. Joshua Hartshorne cautions that their data is age-adjusted, which could introduce biases that may mask the effects of birth order.  Furthermore, the study focuses on the Big Five personality traits: extraversion, emotional stability, agreeableness, conscientiousness and openness to experience. While they found no difference due to birth order on these five personality traits, according to Dr. Hartshorne, whether you accept their conclusion or not depends on “how well you think the Big Five measures personality.”

While this recent publication is, in the words of Dr. Hartshorne, “analytically a tour de force”, it is not the nail-in-the-coffin for this debate. Besides, even if future studies show that birth order has no effect on personality, there are other aspects of life that birth order could and does influence, such as the birth order of one’s spouse and one’s IQ, respectively.

Acknowledgements: Special thanks to Dr. Joshua Hartshorne , a post-doctoral fellow at MIT for his time and expert commentary. Dr. Hartshorne will be joining Boston College’s Department of Psychology in January 2016.

Original Article: Examining the effects of birth order on personality

Further Reading: Birth order stereotypes may not be true

Managing Correspondent: Fernanda Ferreira

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