Engineers Have More Sons, Nurses More Daughters

Bifurcati writes "While it might be irrelevant for many /.ers, a recent study has shown that people in stereotypically male professions (engineering, IT, mathematics, etc) are more likely to have sons than daughters, while nurses, therapists and teachers tend to produce more girls. Based on independent survey data, engineering types produce 140 boys to every 100 girls, while nurses and the like produce 135 girls to 100 boys. The explanation is unclear, but it might have interesting long-term social implications. A more detailed summary of the journal article is available on Illuminating Science."

Comments

Irresponsible statistics

[metachor]

Repeat after me: "Correlation does not imply causality."

Causality

[XanC]

The article seems to imply that by switching to a masculine job, you'll change the sex of your potential children.

I think it's far more likely that it's not what job you're doing, it's what job you tend to want to do.

Summary of the actual article

[call -151]

Both of the linked articles are pretty flismy- the first claims that switching professions may increase the chance of having a child of a particular gender (confusing correlation with causation...) and the second one marvels at the notion that a sequence of children of the same gender is more likely than randomness would suggest (which is already well-established as there is some genetic predisposition towards male sperm having uneven fractions of X and Y chromosome shares).

The actual article (Journal of Theoretical Biology, 233, p589-599 "Engineers have more sons, nurses have more daughters: an evolutionary psychological extension of Baron-Cohen's extreme male brain theory of autism" by Satoshi Kanazawa and Griet Vandermassen and available through Elsevier's Science Direct) came out in December 2004 an is available online for those whose institutions subscribe, notes the following correlations:

This is based on survey data from US professions of around 1500 people. Only some of the professions are categorized as "systemizing" and "empathizing" so presumably the sample size is much smaller than that . The sample size isn't listed directly in the article but it appears to be about 20% of the 1500 with at least one parent so categorized profession, for around 300 people or so. Most professions are neutral in the "systematizing/empathizing" continuum, apparently.

Amoung those with "systemizing occupations" had regression coefficients of .35 with the number of sons and .14 with number of daughters, and those with "empathizing occupations" had coefficients of .27 with #sons and .40 with #daughters. (As a side note, it appears that "empathizing professions" have more reproduction overall, consistent with common myths about lonely geeky engineers...)

From the classification of professions:

Systemizing occupations

• Executative, managerial, adminstrative such as financial managers, analysts, etc.
• Professional: architects, engineers, etc.
• Technicians

Empathizing occupations

• Professional: nurses, speech therapists, teachers, counselors

Presumably other professions are regarded as neutral in this spectrum.

Re:correlation and causations

[cpotoso]

The reason, if any, could be as follows: a couple with more "masculine traits" may stop having children after they get a boy, whereas a "more feminine" couple stops having children after having a girl. Lets enumerate the possibilities.

For the "masculine couple" (please note that the following are not equal in probability!):

BOY, stop

GIRL, BOY, stop

GIRL, GIRL, BOY, stop

etc.

A similar (substituting BOY and GIRL) sequence can be made for the "feminine" couple.

It is easy to see how this would lead to more BOYS or GIRLS in each respective case (on average).

This is one possible explanation of cause.

Re:correlation and causations

[egomaniac]

It is easy to see how this would lead to more BOYS or GIRLS in each respective case (on average).

Not so. Assuming you have a 50-50 chance of it being a boy or a girl, you will end up with 50% boys and 50% girls no matter what contortions you go through to try to influence the outcome.

Look at it another way: pretend these are coin flips rather than childbirths. Your suggestion (that you can alter the odds by when you choose to stop trying) is equivalent to saying that you can bias to heads or tails by deciding when you stop flipping the coin. And, of course, that isn't true -- no matter how many trials you perform or in what order, a fair coin will (on average) deliver 50% heads and 50% tails. One more 50-50 flip won't in any way alter the expected outcome.

It's exactly the same way with childbirth. The first child (we would expect) would be 50% likely to be a boy. The second would be 50% likely to be a boy. The third would be 50% likely to be a boy, and so on ad infinitum. Adding another trial (childbirth) onto the end of the sequence does not change the odds, and on average you would end up with 50% boys and 50% girls.

Of course, this research shows that that naive assumption isn't true, and apparently something is altering the odds. We just don't yet know what.

(And, amusingly enough, I'm to find out my baby's gender in two days. Evidently it's more likely to be a boy...)