“Testosterone levels predict City traders’ profitability”

So says the headline. The article continues:

When City traders have high morning testosterone levels they make more than average profits for the rest of that day, researchers at the University of Cambridge have discovered.

And indeed the studies discussed do show this effect for the 17 traders that they studied (though researchers also note that “high levels of testosterone can lead to irrational decision making”). So what’s wrong with the headline and the quoted claim above? What’s wrong is that they only studied MALE traders. Given that the study’s subject matter is the effect of sex-linked hormones, it would seem especially important to study both sexes before making general claims. On the good side, the article makes no claims at all about this showing why women are less likely to get high-powered financial careers. But I wouldn’t be at all surprised to see someone else citing it in support of that claim. (Thanks for the link, Christine!)