Validity of birth order psychology

Is there any validity to the psychology of birth order?

Opinion only, but I can’t see how there wouldn’t be some effect of birth order on psychology. Especially for the first child and likely the last one. I’m a parent and a friend of other parents, and in my (admittedly small for statistical purposes) sample size, it’s pretty clear that parenting is much more conservative for the first child, because you have no experience and take a more cautious attitude. Also, there’s no choice but to divide your love and attention among multiple children after the first, so that’s something the second and beyond children are born into.

Also, personal experience looking at siblings in various families of my generation seem to back this up, but again that’s highly unscientific.

Perhaps this is being very selective but consider these pairs of older brothers versus younger brothers:

  1. Ron Howard … Clint Howard
  2. Pat Weaver - NBC Executive - created Today Show (among others) - his younger brother was Doodles Weaver
  3. Dick Van Dyke…Jerry VanDyke
    Hmm do I detect a pattern here?

According to my old psych professor, first-born children tend to have higher IQs than later-born children. This difference is very small, however: maybe about 1 IQ point on average.

He said a few other things about how birth order affects psychology, but unfortunately I don’t remember any more.

Depends what you’re talking about. Theres research findings whihc are fairly well supported, then theres theories on it that more developed from clinical practise than based on research as such.

Bit more dubious about them myself.


Can a 1 IQ point difference even be established to a degree of statistical significance?

Dr. Kevin Leman has written some interesting stuff on book order if you ever want to read up on it.

Is it valid? No.

The best study ever done in birth order psychology was done by Ernst and Angst in 1980, entitled “Birth Order : Its Influence On Personality”. Not only did they perform a meta-analysis of all existing data (excluding some studies with flawed methodologies) they also performed the largest ever study of birth order, with around 8000 subjects. Their conclusion? It went along the lines of “studies of this kind are a waste of time and money.” The only significant effect found was a very slight drop in masculinity for later-borns.

Frank Sulloway also performed a meta-analysis of the birth order data in his 1995 book Born to Rebel. The method he used for the meta-analysis has been criticized as he includes data that didn’t allow for socio-economic status effects (as lower-class families are larger on average), and he also includes different data-sets from the one study as separate studies. His result? He finds later-borns score higher on the O factor of the big five personality traits, openness to experience. Also, through his very large qualitative analysis of various revolutions he suggests that later-borns have a higher propensity to participate in revolutionary thought. I’m quite skeptical of these claims due to the potential for confirmation bias in qualitative analysis. Also worth noting is that Sulloway did not make reference of the Ernst and Angst study in his book.

Judith Rich Harris, author of The Nurture Assumption, has written a number of essays on birth order. (link) I think they sum up the problems with the field quite well. So in short, no, it’s not valid.

I am the third born of four children. The middle triplet, and also the middle son.

Yes. Your mileage may vary.