The Surprising Way Birth Order Influences the INTJ Personality

an INTJ personality with her siblings in birth order

Siblings: love them or hate them, there are plenty of scientists who theorize that you’re made by them, in the sense that your birth order affects the type of adult you’ll grow up to be. It’s an interesting theory and one that we at Truity have been studying for a few months now — with some surprising results.

A few weeks ago, we published our full analysis of the correlation between birth order and personality type, and a breakdown of the findings for INFJs. These data are based on a study of 5,747 Truity readers, correlating their personality type with their position in their family of origin.

This week, we’re shining the spotlight on INTJs. Here’s what we found.

INTJs Are Much More Likely to Be Firstborns

Statistically, INTJs are much more likely to be the firstborn of the family (+17.5%) than if personality happened by chance. At the same time, they are much less likely to be a middle child (-20.00%) or the baby of the family (-10.00%).

In terms of individual traits, eldest children were much more likely to be Thinkers (+3.04%) rather than Feelers (-2.92%) and Judgers (+4.441%) rather than Perceivers (-3.76%). These findings support conventional birth-order theory which posits firstborns as responsible, conscientious, balanced, controlling, and trustworthy — traits that are associated with a Thinking-Judging preference according to the personality theory of Isabel Briggs Myers.

Is there something about growing up as the eldest that nudges people to become more responsible and achievement-oriented than they might otherwise be? Our INTJ readers had some thoughts:

“Being the first born, there were huge expectations on results, planning, and taking care of other responsibilities — like younger siblings or help at home,” said one 30-year-old INTJ. “There was a lot of pressure to have great grades and at the same time be ahead of all chores and homework, to excel at school (be the best), and to take things seriously and responsibly.”


Like what you’re reading? Subscribe to our INTJ-only newsletter here.


A 71-year-old respondent agrees. “The need for independence and autonomy is very strong in INTJs,”  she said. “With a firstborn child, the parents are on a whole new learning curve. So they enhance the purpose of the INTJ child with the need to learn, grow, and achieve.”

INTJs Are Less Likely to Have Siblings

According to our analysis, being an only child has the most pronounced impact on individual personality traits. Only children are much more likely to be Thinkers (+8.23%) rather than Feelers (-7.89%), and Intuitives (+3.62%) rather than Sensors (-10.98%) than if birth order had no impact on personality. They are also more likely to be Perceivers (+6.91%) rather than Judgers (-8.3%).

Given these findings, it’s no surprise to see INTPs topping the list as the “type most likely” to be only children (32% more likely than if personality happened by chance). But INTJs, despite being Judgers, were also overrepresented in this category. Our research showed that INTJs are 15% more likely to have grown up as only children, which is the second-highest positive association after INTPs.

What’s going on here? Some psychologists have theorized that only children are like “super firstborns,” with all the typical traits of a firstborn child in even higher relief. So perhaps we can observe similar forces at work when considering the INTJ eldest and the INTJ only.

Our respondents seemed to think so. Across the board, they expressed a firm conviction that being an only child gave them an extra nudge towards introspection, as well as the INTJ tendency to chart their own course in the world:

“I think being the only child has forced me to grow up faster and be more mature,” said a 17-year-old INTJ respondent. “With no one close to talk to growing up, I think I became more introverted, relying on myself.”

A 26-year-old agrees. “Without any sibling to go through the same experience as me, I learned to be independent and think for myself in overcoming challenges,” she said. “Being an independent thinker, I am attracted to understanding abstract concepts/theories and solving complex problems. Subjects such as philosophy, sociology, and psychology intrigue me as there are no definite answers. At the same time, I like to lead others and help people see the vision I see.”

One 52-year-old INTJ puts it succinctly: “Being an only child means you spend more time alone in your inner world.”

The Rare INTJ Middle Child

According to our data, middle children are much more likely to be Extraverts (+5.39%) rather than Introverts (-5.74%), more likely to be Sensors (+3.43%) rather than Intuitives (-1.13%), and much more likely to be Feelers (+6.93%) rather than Judgers (-7.23%). So you won’t be surprised to learn that INTJs are 30% less likely to be middle children than if personality had no connection with birth order — one of the most striking data points we found in the entire study.

Now, just because INTJs are grossly underrepresented as middle children doesn’t mean they don’t exist. But what’s interesting about our “sandwich” INTJs is just how many of them reported feeling conflicted in their role as mediator. Unlike firstborn INTJs, who overall seemed to be comfortable in their leadership role, many of our middles believed that they did not fit the “peacekeeper” mold at all.

“I felt a lot of internal conflict between being an INTJ and a middle child,” said one 29-year-old INTJ. “I felt like I was expected to function as a middle child by following my older sister around and leading my younger sister, but I really just wanted to play by myself…I struggled to find an identity until my college years, which is when I learned about the MBTI model and my personality type. Even then, I struggled for a long time to accept my type because it seemed to conflict with my training to be a peacemaker.”

This 25-year-old agrees: “I am probably more gregarious and social compared to an INTJ who is an only child, but that’s about it,” he said. “I always had the feeling of being different. In my family, I was very independent and refractory to authority, and at school, I felt like I was older than my fellows in terms of maturity. I was a child but was not very childish. My inner worldview was out of step from the others, and I was often misunderstood.”

So, Did Your Birth Order Make You an INTJ?

Myers and Briggs believed that personality is part of our makeup when we arrive at birth. However, our research does suggest that your birth order may at least nudge you in a particular direction. For the most part, our INTJ readers agree.

Overall, our INTJ respondents supported the notion that you may be born with a certain personality, but from the moment you are born, your family goes to work on you — encouraging the behavior that works and discouraging the behavior that doesn’t. They were also open to the idea that what works and what doesn’t work, so far as parental expectations are concerned, may depend on your position in the family tree. Our research certainly seems to suggest that eldest children are rewarded for “TJ” type behavior, whereas middles are encouraged to explore their peacekeeping side. This might explain why INTJs felt so conflicted in this role.   

The bottom line is that there likely are layers of learned behavior on top of our innate personality preferences, and birth order is just one of those layers. Each one will affect our behaviors and how we present ourselves in the world. We hope our research adds another dimension to the question of why we are the way we are — but it’s only one part of puzzle, and there’s still a lot of work to do.

INTJs, how do you fit in with these findings? Let us know in the comments below.

You might like:

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.