Human Sex Ratio Doesn't Run in Families
By Bryan Caplan
I have three children, all sons. On a gut level, I feel like there’s a systematic factor at work. It must be my overpowering machismo, right? But it looks like my gut is dead wrong. At least in the NLSY, sex ratio doesn’t run in families. If you simply look the frequencies of BB, BG, GB, and GG…
For the first two children, families heterogeneous by sex were more likely than expected in an independence constant probability model.
If you estimate a full model with a gender-biased stopping rule (i.e., if you get GG, try again), the pure chance model checks out:
In this model-fitting exercise, there was a straightforward and unambiguous answer to the sex composition question when parameters for parental stopping behavior separated that process from the sex probabilities. The answer to the question, “Does having boys or girls run in the family,” was clearly “No.”
Bottom line: If you want girl, marrying someone from a family with a low male/female ratio won’t help you. Try sperm sortation instead.