Only children can't share. First-borns are bossy. And the youngest child gets away with murder. We all know the stereotypes connecting personality with birth order, and no matter where you sit in your family tree, you likely have some assumptions about how your position in your family helped to shape your personality. 

But is it true that your birth position can drive your personality and behavior? We wanted to find out. So, we asked visitors taking our TypeFinder Personality Test (based on Myers and Briggs' typology) to share their family history. Some 5,747 people generously responded, and we correlated those responses with volunteers' personality types to see what trends, if any, we could uncover.

What do you think we found? Are first-borns really our natural leaders? Are sandwich kids as harmony-oriented and fairness-loving as we think they are? Do the babies of the family enjoy more independence than their older siblings—and the confidence that goes along with it?

I won’t leave you in suspense—the stereotypes are, by and large, absolutely true. When we analyzed the data for all 16 personality types in Myers and Briggs' system, we found some startlingly familiar trends in the four preferences and birth order.

Here’s what we discovered:

First Borns Take the Lead

If you’re looking for a natural leader, look no further than your firstborn. Being the oldest translates into certain family responsibilities that require leadership skills from an early age. Parents tend to invest much more time in their first borns, and expect them to serve as role models to their younger siblings. As a result, parents describe their first-born children as:

  • Responsible
  • Conscientious
  • Diligent
  • Structured
  • Achievers, in terms of educational and career achievement.

Looking at this list of traits, we can predict that oldest children will favor fact-oriented personality traits, namely Thinking (in Myers and Briggs' theory, this indicates a person who makes decisions based on logic) and Judging (the desire to be organized and have decisions made). TJs like rules and guidelines, are conscientious, and respect and trust authority, which explains why they’re overrepresented in the leadership and management ranks of corporate America.

Does the data support these assumptions? Yes—and the results are striking. When we looked at our respondents’ personality results, first-borns, by a fair margin, were Thinker-Judgers. Roughly 19.5 percent more ESTJs were first-borns than we would expect to see if birth order and personality were completely uncorrelated; for INTJs, the figure is 17.5 percent.

Bringing up the rear are the ESTPs, ESFPs and ISFPs with far fewer of these personalities being a firstborn child than we would expect to see if personality traits were distributed by chance. It’s not easy being a free-wheeling Perceiver when your parents are overwhelming you with so much structure and attention.

Type Prevalence Among First-Born Children (Percentage Compared to Expected)


Middle Kids Make Connections

Middle kids are in a bit of a bind. Unlike firstborns, they never had the parents to themselves, but they didn’t get to enjoy all the fuss and privileges of the youngest child either. They get the short end of the stick in terms of parental attention—and are perceived as being eager to please and impress as a result. Here are some of the stereotypical traits we expect of middle children:

  • Easy going
  • People-pleasers
  • Thrive on friendships
  • Gold-star negotiating skills
  • Peacemakers

The prediction here is that middles would exhibit high Feeling preferences, making decisions based on compassion and what is important to people. You might also expect them to lean towards Perceiving (over Judging) since there’s an advantage to being easy-going and flexible as you navigate the middle ground.

So what does the data show? You guessed it—there’s a strong likelihood that a middle child will be a Feeler. Way out in front, ISFP types are a whole 41.67 percent more likely to be a middle child than chance would suggest, with ESFP and ISFJ following close behind. We do note the relatively small sample size for ISFPs, which means these results are more prone to error. But, even if the trend is less exaggerated than these data show, it certainly signals an area ripe for further exploration.

For middles, there’s a negative correlation with Thinking types across the board. In terms of the individual traits, middle kids are 6.93 percent more likely to be Feelers, and 7.23 percent less likely to be Thinkers than if personality had no relationship with your position in the family hierarchy. This is significant!

There’s another trait to consider here and that’s Extraversion. All that floundering in the middle often leads sandwich children to develop many and varied friendships, since parental attention is normally devoted to the firstborn or the baby of the family. Introverts typically find it less appealing to maintain a large network of friends, so it’s no surprise to learn that middles are more likely to be Extraverts than Introverts.

Or, to put it another way, locating an INTJ who is also a middle would be an extremely rare find. Which explains why INTJs are a full 30 percent less likely to be middle kids than if personality happened by chance!

Type Prevalence Among MIddle Children (Percentage Compared to Expected)


Youngests Just Want to Have Fun

Although the youngest gets the “baby bonus” of parental coddling, it’s not all easy for these kids. Parents tend to be less impressed by their accomplishments because they’ve “been there, done that” with older children. And there’s just no time left to police these kids, so they get to play fast and loose with the household rules. This means that youngest children are more willing to take risks than older kids, and they often develop “out there” ways to attract attention, such as being the family clown.

Other stereotypical youngest-child traits include:

  • Uncomplicated
  • Outgoing
  • Attention-hungry
  • Rebellious
  • Self centered

What’s the personality prediction here? We reckon that last-borns would be Extraverted and Perceiving for sure, and may exhibit a slight leaning towards Sensing (living in the moment) over Intuition (future focused), although the latter is a tougher call.

Once again, the data shows this prediction to be true. ESFPs and ESTPs are 22.22 percent and 14.29 percent respectively more likely to be younger children than if personality had no connection with birth order. The opposite is true for NTJs, who are significantly underrepresented in the baby-of-the-family group.

Overall, though, being the youngest child seemed to have the least impact on individual personality traits.

Type Prevalence Among Youngest Children (Percentage Compared to Expected)


What About Onlies?

Only children occupy a special place. They enjoy the full attention of their parents for their entire lives, and do not have to share resources such as their parents' time or money with anyone. Not only do they get more attention than siblings, they typically have adults rather than peers to latch onto and learn from. Essentially, this makes the only child something like a "super-firstborn" but with a bit more freewheeling self-confidence thrown in—these kids can take more risks than firstborns as they have exclusive access to the parental safety net.

In terms of specific traits, onlies are expected to be:

  • Confident
  • Perfectionist
  • Independent
  • Outside the box thinkers
  • Wise beyond their years

The prediction, then, is for onlies to be Thinkers like firstborns, but with less propensity for Judging. In fact, we might speculate a preference for Perceiving. Without siblings to boss around, onlies can afford to be a bit less structured than firstborns.

There are a few interesting trends to take note of here.

First, our ESTP respondents were 100 percent more likely to be only children than if personality and birth order were completely uncorrelated. This is an extraordinary result, and possibly one that should be taken with a grain of salt since ESTPs— and SPs generally—were woefully underrepresented in our respondent group. (The data potentially tells us more about an SP’s attitude to surveys than it does about their birth order personality, so we’re not reading too much into this finding.)

But there are some other trends which are really pronounced—for instance, there are 32 percent more INTP only children than we would expect to see by chance. On the flip side, ESFPs and INFJs are significantly less likely to have grown up as only children, by 44 percent and 34 percent respectively.

Type Prevalence Among Only Children (Percentage Compared to Expected)


Across the board, it seems that being an only child has the most impact on individual personality traits of any family position. Onlies are much more likely to be Thinkers (rather than Feelers), perhaps because they're not under as much pressure to be agreeable with no siblings about. They're also more likely to be Perceivers (rather than Judgers), and slightly more likely to be Intuitives (rather than Sensors), although the reasons for this difference are harder to guess at. It could be that only children get more time to daydream, wonder, and explore in their smaller, less busy families—or it could be that the complexity of parenting an NTP kid leads parents to decide that one is enough!

As to Introversion/ Extraversion, you might theorize that only children would be more introverted since they’re lacking sibling company. Or, maybe they'd be more extraverted, since they have to make more effort to socialize. In fact, the data shows a very slight Extraversion bias—but the data here is underwhelming. Being an only child doesn’t appear to have a significant impact on Introversion versus Extraversion at all.

The Meaning of Birth Order

We did this analysis to see if there were any trends in birth order in relationship to personality type. We were curious to know whether there were certain types that were more likely to occur in a particular birth position, or if particular preferences were influenced by the family structure. What’s fascinating is that overall, the data suggests that what we assume about birth order and personality is mostly true—whether you're firstborn, middle child, last-born, or only child, birth order can have a big effect on your personality in all the ways that parents have observed.

One discovery that we found especially interesting is that some types are much more (or much less) likely to occur in a particular birth position. INTJs, for instance, are unlikely to be middle children. ESTJs are likely to be firstborns. INTPs are often only children and ESFPs are almost never only children.

So, perhaps these findings can help you to better understand what makes you (and your siblings!) who you are. In the meantime, psychologists continue to chip away at an understanding of how our personalities are formed. Birth order may only be a small part of what makes us who we are, but it seems to be a significant one.

Which leaves us with a final question: how do you think your birth order influenced your personality type?

Molly Owens
Molly Owens is the founder and CEO of Truity. She is a graduate of UC Berkeley and holds a master's degree in counseling psychology. She began working with personality assessments in 2006, and in 2012 founded Truity with the goal of making robust, scientifically validated assessments more accessible and user-friendly. Molly is an ENTP and lives in the San Francisco Bay Area, where she enjoys elaborate cooking projects, murder mysteries, and exploring with her husband and son.