Diving Down the Rabbit Hole: Trying to Counter Birth Order Theory

Trying to convince people that birth order theory is not legitimate science is rather like trying to convince people that astrology is not real science--or, for that matter, that global warming is more problematic than true believers will countenance. All those missing correlations are swept away by the force of the theory. 

The problem with birth order theory is how much it depends on people finding the correlations they expect to find. I often encourage students to avoid writing about birth order theory simply because they make the same mistake as Sulloway: they locate and label a personality trait within a famous person, then assume that the famous person must be a firstborn, middle, or later-born child, often without even bothering to Google search if they are correct.

Only occasionally have I had a student admit, Wow, the research doesn't justify any conclusions at all!

Most birth order theory comes down to interpretation: how existing behavior fits people's expectations. Take, for example, an event that never occurred in my own family: a parent gifting a teen with a car. When the event occurs to the firstborn, the interpretation is that the parents are applauding the oldest child's maturity and good work habits; to the middle child, trying to making up for lack of attention; to the youngest child, spoiling.

But the act is the same.

In 2015, Julia M. Rohrer, Boris Egloff, and Stefan C. Schmukle from the University of Leipzig and Johannes Gutenberg University of Mainz performed a lengthy investigation of birth order and its possible ties to personality. They used longitudinal data from a Great Britain study, data from an extensive study by the US Bureau of Labor Statistics, and data from a German survey of households that started in 1997. They relied on within-family and independent assessments (within-family assessments tend to depend on "existing beliefs and stereotypes as well as contrast effects"--that is, people within families tend to define themselves by how they are like and different from each other using the rhetoric at hand). The researchers also made within-family and between family assessments. For IQ, they used self-referencing and outside testings.

They discovered that the only measurable, consistent difference in birth order is IQ testing--and even that is negligible. Older siblings tend to test higher than younger. Don't get too cocky, older siblings! Not only is the difference minor, Rohrer, Egloff, and Schmukle reference outside studies that postulate that (1) "older siblings profit intellectually from being 'teachers' to younger siblings"; (2) later-born children are prone to "slightly underestimating [their intelligence] and firstborn children slightly overestimating their actual cognitive abilities." There is an odd but consistent correlation between how intelligent people believe themselves to be and how well they test.

Other than IQ testing, the study found that "birth order position had no significant effect on extraversion, emotional stability, agreeableness or conscientiousness." The study divided the fifth of the Big Five personality traits--openness--into IQ (see above) and imagination. They found that birth order had no effect on imagination. 

The tone of the study is extraordinarily dry, only dropping into wryness towards the very end: "Brief self-report measures are also generally sensitive to detecting birth-order effects when such effects indeed exist."

In other words, within a family, family members will notice if a particular family member is good with puzzles or adept at getting along at parties or quick to spot humor in a situation. The same family is quick to discern how this relates to the person's position, or niche, within the family and to provide an interpretation: i.e. so-and-so gets along well at parties because he or she got more attention from our parents. Voila! Birth order theory is true!

However, the study's conclusion is unequivocal, if staid:  

"The central prediction of the Family Niche Theory with regard to personality could not be confirmed by our analyses . . . to conclude, birth order position seems to have only a small impact on who we become."

For those of you who are gnashing your teeth, I do have an alternative suggestion, having to do with families as blueprints--post coming at a much later date . . .