Experts from the University of Mainz and University of Leipzig sought to determine the correlation between birth order and personality—a question that researchers have been investigating for more than 100 years.
The study, which was recently published in the Proceedings of the National Academy of Sciences, examined more than 20,000 adults from Great Britain, Germany, and the United States through self-reported surveys.
The psychologists behind the research ultimately concluded that the "big five" traits (conscientiousness, extroversion, emotional stability, agreeableness, and openness to experience) are not impacted by birth order.
However, researchers did note one interesting correlation: Firstborns were more likely to report an abundant vocabulary, and they more easily understood abstract ideas.
It's possible that prior research did not take into account the ages of children when determining birth order's potential impacts, the researchers said.
"We might wrongly confuse age effects with birth order effects," noted lead researcher Julia Rohrer of the University of Leipzig. "The relevant question for detecting a birth order effect would rather be: 'Will my younger sister be at my level of conscientiousness when she is as old as I am now?'"
Caitlin St John is an Editorial Assistant for Parents.com who splits her time between New York City and her hometown on Long Island. Follow her on Twitter: @CAITYstjohn.