Anecdotally, almost every parent has noticed the personality differences that arise in their children. How is it that Rachel, the firstborn, seems to have such different personality characteristics than her younger brother, raised in the same house by the same parents just two years apart?

Alfred Adler, an Austrian psychotherapist, was the first researcher to study these natural differences. He believed that our birth order within a family played a significant role in the type of adult we would become. Firstborns were observed to be goal-oriented and perfectionists, for example, whereas their younger siblings were judged to be more affectionate, socially oriented and carefree.

But it is not necessarily the case that a firstborn drops out of his mother's womb with all the characteristics of a leader.

In 1953, a researcher called Rudolf Dreikurs noticed that, in practice, parents never treat two children alike but rather behave very differently towards each child depending on their position in the family hierarchy. So if the firstborn has leadership qualities, it's because his parents treated him as the apple of their eyes - and this influence shaped the child's attitude and behavior.

The Birth Order Hypothesis

Here's what birth order advocates have to say about personality characteristics, by reference to a person's position within the family - plus a little speculation as to how Adler's observations might translate to Myers and Briggs' theory of personality types.


Firstborns are rule-abiding overachievers who respect and trust authority. They often appear as perfectionists, are academically more successful than their younger siblings, and are typically judged as more serious, seclusive and cautious than later borns. Adler describes them as:

  • Conscientious
  • Reliable
  • Disciplined
  • Independent
  • Seclusive
  • Achievement-oriented

Mapping this to personality types, we would expect older siblings to have a greater probability of having an Introverted, Thinking and Judging personality. Parents typically set more stringent standards for their firstborns, which means that firstborn children are more likely to be willing to work hard to please their parents, developing the characteristics of a structured, reliable achiever.

Middle Children

Caught between the oldest and the youngest, the middle child often has trouble finding her place in the family and may lose her sense of self. Middles excel at peacekeeping and are generally judged to be non-confrontational, non-competitive, diplomatic and compromising. Adler describes them as:

  • Sociable
  • People-oriented
  • Nurturing
  • Easygoing
  • Loyal
  • Independent

From these observed characteristics, we speculate that middle children would prefer Perceiving to Judging and Feeling to Thinking. Perceivers seek to understand life rather than control it, and are generally even-tempered and flexible. Feelers, like middle children, appreciate harmony, sensibility and human relationships.


The baby of the family tends to be the most idealistic and free-spirited due to their parents' increasingly relaxed attitude towards parenting the second (third, fourth) time around. They are judged to be more popular, more affectionate and more persuasive than their older siblings. Adler describes last-borns as:

  • Outgoing
  • Agreeable
  • Spontaneous
  • Adventurous
  • Affectionate
  • Manipulative (to attract their parent's attention)

Similar to middle children, we would expect younger siblings to exhibit a preference for Feeling and Perceiving over Thinking and Judging. As the most outgoing of the bunch, we might also expect them to score highly as Extraverts. Extraverted Perceiving types tend to live in a particularly flexible and spontaneous way, preferring liberty and adventure to rules and restraints.

What Does the Research Say?

Is there any proof that older children are more likely to be Judgers, or younger children Perceivers, or are we inventing hindsight rationalizations for something that doesn't exist?

Unfortunately, there's no clear answer to this question. Research is scarce, and what little there is uses such small sample sizes that it is difficult to draw any real conclusions.

The primary study, published in The Family Journal: Counseling and Therapy for Couple and Families in 1998, sought to measure the influence of birth order and other factors on the Myers-Briggs dimensions of Introversion/Extraversion and Judging/Perceiving for 144 study participants. Known as the "attitude" scales, I/E and J/P preferences determine how a person orients with the world and communicates with the people around them. According to the researchers, a person's preference on these scales is likely to be influenced by parenting style and, therefore, birth order, whereas a person's preference on the mental activity (S/N) and decision-making (T/F) scales are not.

The researchers identified parenting style as having a significant main effect on both the Extraversion and Judging functions. Firstborns had significantly higher Introversion and Judging scores than did middleborns and last-borns. The more authoritarian the parenting style, the greater the I and J score.

Conversely, more middleborns and last-borns had higher mean scores on the Extraversion and Perceiving scales - consistent with Adler's findings.

So What Does It All Mean?

Personality is not a fixed list of attributes, but instead is a complex interaction of attributes that depend on the situation we find ourselves in. It may be that birth order stereotypes hold true in the home, while we are children. But away from parental and sibling influence, other variables may come into play.

Modern research suggests that Adlerian birth order theories may be too simple. More recently, scientists have been examining the role of other influences on personality, such as gender, genetics, age spacing and socioeconomic factors. Birth order is just one lurking variable among many.

The bottom line is, no one really knows the impact that birth order has on personality type, and there's a desperate need for research.

Until then, the birth order mystery remains unresolved.

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.