A year or so ago I heard about a couple of papers by Satoshi Kanazawa on "Engineers have more sons, nurses have more daughters" and "Beautiful parents have more daughters." The titles surprised me, because in my acquaintance with such data, I’d seen very little evidence of sex ratios at birth varying much at all, certainly not by 26% as was claimed in one of these papers. I looked into it and indeed it turned out that the findings could be explained as statistical artifacts–the key errors were, in one of the studies, controlling for intermediate outcomes and, in the other study, reporting only one of multiple potential hypothesis tests. At the time, I felt that a key weakness of the research was that it did not include collaboration with statisticians, experimental psychologists, or others who are aware of these issues.
I did my duty and wrote a letter which was published in the Journal of Theoretical Biology. (I also emailed Kanazawa a copy but didn’t hear back from him.) There things stood until yesterday when I saw in Tyler Cowen’s blog that Kanazawa had written an article in Psychology Today repeating the claim, "Americans who are rated "very attractive" have a 56 percent chance of having a daughter for their first child, compared with 48 percent for everyone else." And, even more amazingly (to me), Kanazawa is publishing a book called "Why Beautiful People Have More Daughters." The work has also been publicized in various places, including a positive mention by Stephen Dubner here (and a more mocking mention here).
OK, now to get to my question. Kanazawa’s conjectures have not been demonstrated statistically. (For example, the claim about beautiful parents having more daughters was barely statistically significant and was one of many possible comparisons that could’ve been done with those data.) So it’s a little disturbing to see this as presented as "true, supported by documented scientific evidence." On the other hand, their claim might be true. It would be more scientifically appropriate for Kanazawa to present these results as "speculations which are supported by data," but maybe Psychology Today expects a different sort of writing?
I just don’t know how to think about this. It’s clear to me how journalists, bloggers, and reviewers should react: the should discuss this work with skepticism. The trouble is that the papers were published in a reputable journal (J. Theor. Biology), and a journalist/blogger/reviewer who does not happen to see my critique would naturally tend to trust the result. (I was only tipped off because I’d already read a bit in the area of sex ratios, for no other reason than that I’ve used boy and girl births as a teaching example. This was essentially a bit of Bayesian reasoning by me, that Kanazawa conclusions didn’t match my priors, leading me to look more carefully at his reasoning.) So I can’t really blame the editors of Psychology Today, or maybe even the editors at Perigee Books for not knowing any better.
But should I blame Kanazawa? I don’t want to be dismissive of scientific speculation–I don’t like the idea of statistican as censor–so maybe there would be a way for him to present more of the full statistical story in his book (for example, in the beauty-and-daughters study, a graph with the proportion of girls born to people of all five beauty categories–rather than just comparing categories 1-4 to category 5–along with the beauty assessments from all three waves of the study). It’s a tough call to decide how to present speculative findings.