What birth order can and cannot predict has been a topic of interest among researchers for some time now — more than 100 years, by German researchers' count. These same researchers recently conducted a study, published in PNAS, on the effects birth order has on personality traits — turns out the effects may be much smaller than we think.

The traits we’re referring to are ones you’ve likely heard of: first-borns grow up to be perfectionists; middle children develop a talent for diplomacy; and the youngest are rebels. Some of these traits, namely those related to IQ, stemmed from earlier research that showed oldest kids scoring highest on intelligence tests, Time reported. But just this past July, in the largest study on birth order to date, researchers found this order had little effect on personality and IQ.

In an attempt to bridge these inconsistent findings, researchers from Leipzig University and the Johannes Gutenberg University Mainz in Germany analyzed data collected from more than 20,000 adults from Germany, the U.S., and UK: 10,457 Germans, 5,240 Americans, and 4,489 British people. This way, Time explained, researchers could compare both people within their families and those of “other sibling sets.”

Within this data were participants’ answers regarding their birth order, as well as their IQ, self-reported intelligence, imagination, and the Big Five Personality Traits: openness, conscientiousness, extraversion, agreeableness, and emotional stability. Researchers found that central personality traits, such as extraversion, emotional stability, agreeableness, and conscientiousness are not affected by birth order after all. First-borns, however, were more likely to rate their self-intellect higher than other siblings; they reported a rich vocabulary and less difficulty understanding abstract ideas.

"This effect on intelligence replicates very well in large samples, but it is barely meaningful on the individual level, because it is extremely small," study co-author Stefan C. Schmukle said in a press release. "And even though mean scores on intelligence decline, in four out of 10 cases the later-born is still smarter than his or her older siblings."

Schmukle added "the real news" of the present study is that there are no substantial effects of birth order on any of the personality traits they examined (with the exception of intellect). In the study’s footnotes, Rohrer and her colleagues suggest that parental age "might be a potential confounding variable that is causing the effects on intelligence and intellect." They also considered that "birth order effects could be visible within the family, but might not affect behavior and relationships outside of this context."

If birth order doesn’t really determine your personality, then what does it predict? According to some studies, it may still predict future health outcomes. A recent study published in JAMA Opthalmology found that nearsightedness was more prevalent in first-born children, while two separate studies have suggested that first-borns are more likely to be obese, particularly first-born girls.

On the other hand, youngest siblings were 18 percent more likely to commit suicide than first-borns in a Swedish study conducted in 2014. The researchers said they needed to study the finding further, but they were still important to be considered an "early-life circumstance that determines mental health across the life course."

As for middle children, some experts find that they’re often more successful than their siblings, in terms of empathy, independence, articulacy, creativity, and an eagerness to please.

Source: Rohrer JM, Egloff B, Schmukle SC. Examining the effects of birth order on personality. Proceedings of the National Academy of Sciences of the United States of America. 2015.