But in this case, correlation does imply causation, and here’s why: If you take 3 million people, have them all flip coins, and divide them into two groups according to whether their coins came up heads or tails, then the two groups are going to look statistically identical in every way—same average income, same average intelligence, same average height. That’s called the law of large numbers, and it works for two reasons—first, the sample size is huge, and second, coin flips are random. Now do the same thing, dividing your 3 million people according to the gender of their last-born child. The same thing happens—parents of boys are going to be statistically identical in every way to parents of girls, because you’ve still got a huge sample size and because the sex of a child is as random as a coin flip. Since everything else is equal, the only thing that can be causing the difference in divorce rates is the gender of the children.
Still, I’d like to see the cross tabs. If you adjust for all the factors that tend to make people happy (and therefore less likely to divorce) – stuff like income, education, marital status, health, etc. – is the effect still present? In other words, do married women with $100,000 jobs, and Master’s degrees, and husbands, and clean bills of health, and daughters still get divorced more often than women with $100,000 jobs, and Master’s degrees, and husbands, and clean bills of health, and sons?
If so, then I will quietly begin to weep.
One tangent before I change a diaper: a number of studies suggest that boy fetuses are more likely to miscarry under times of stress. Natural and social catastrophes (like 9/11), unemployment, extremely hot climates, and poor diets have all been show to lower the boy to girl birth ratio. Call women “the weaker sex” all you want, but exactly the opposite is true in the womb. Boy fetuses need more support and are less likely to survive without it. Might this tie back into the notion that parents of boys are happier on average than parents of girls? If they’re less likely to live in high stress environments or have experienced any of the above calamities, then it would make sense.
Now, on to yellow-green poop.