Study Suggests Birth Order Will Not Predict Personality

Photo of a family of fourOldest children have long basked in the glow of myths about their intelligence, friendliness, and willingness to please their parents. They can even point to the fact that oldest children have won more Nobel Prizes than other groups.

Now, a new study backs up oldest children who think they might be just a bit smarter than their younger siblings. Researchers have found a tiny IQ difference between oldest children and their siblings, as well as very small differences in personality. The differences, researchers say, are not large enough to produce significant differences based on birth order alone.

Why Birth Order Matters Less Than We Think

Researchers tracked 377,000 American high schoolers, making this the largest study of differences based on birth order that has been conducted. The team controlled for factors that might alter the data, such as family size and structure. Rather than comparing children to their siblings or asking participants about their subjective experiences, researchers compared each child to the larger cohort, reducing the risk of skewed data. Previous studies have asked older children if they are more responsible than younger siblings or asked parents for subjective assessments, approaches that are generally less reliable.

Researchers found that firstborn children had an IQ that was one point higher, on average, than that of their younger siblings. Though the difference was pronounced enough to be statistically significant, the study’s authors say that it is meaningless and cannot account for or predict differences in achievement or academic prowess.

The study also found very small differences in personality. Oldest children tended to be less anxious, more introverted, more conscientious, and more agreeable. The correlation, however, was a mere .02, where 0 indicates no correlation at all. Thus, a child’s birth order is only slightly better than chance at predicting his or her personality.

A number of books promise to help parents parent more effectively based on the birth order of their children. The study’s authors say that this is a misguided strategy and that birth order will not provide parents with clues to more effective parenting.


  1. Firstborn children have ‘infinitesimally small’ IQ lead over siblings. (2015, July 21). Retrieved from
  2. Scientists have discovered whether being a first, second or third child makes a difference. (2015, July 17). Retrieved from

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  • Bekkah


    July 22nd, 2015 at 3:19 PM

    Thank goodness someone finally came to their senses and understands that it is all about the child, and no matter what order they were born in either!

  • Jane


    July 23rd, 2015 at 11:40 AM

    Really? Because I look at my own nephews and the birth order predictions are pretty evident in them. The oldest has always been the more motivated one, the middle is looking for someone to give him some attention and the baby never has to follow any of the rules. That pretty much sounds true to form to me!

  • Steven


    July 25th, 2015 at 6:44 PM

    Yep they are pretty spot on in my family too

  • ridley


    July 26th, 2015 at 9:39 AM

    The only way that I think that it could possibly influence personality traits is if this is how the parents have treated these children from the start. If they went into parenthood thinking that this child will be this way and this child will be that way, then of course the kids are going to grow into that role because this is what has always been expected or projected onto them.

  • Rem


    July 27th, 2015 at 5:06 PM

    I always did think that this was just a little too cut and dry to explain the differences between siblings. I mean, there are always going to be those little things that will set you apart, things that make one parent crazy and make the other love you even more. That is all just a part of having your own role within the family.

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