James Trefil and Sarah Swartz raise an important issue in physics education—the underrepresentation of women in physics. They particularly focus on the nonproportional decline of women—as compared with men—between high school physics and an undergraduate physics degree. In their article, Trefil and Swartz present important data clearly showing that the percentage of women in physics is particularly low; the authors argue that there is no obvious reason why physics should do worse than other fields, such as mathematics. They deduce from the data that the cause of the decline is women’s undergraduate physics experience. Although the authors do not claim to have found a full explanation as to why the percentage of women declines so much, they hypothesize that gender bias in textbook problems might be a contributor—that is, that textbook problems assume prior knowledge more likely to be possessed by male than female students.

Unfortunately, the authors do not offer any research or data that support their hypothesis. That might have been fine for an opinion piece, but we are disappointed to see such extensive speculation in a PHYSICS TODAY article. Physics education research is not different from other research: Claims must be backed up with data and studies. Instead, Trefil and Swartz offer examples from unnamed sources—five from a “popular university physics text” and two from a “popular calculus textbook”—that are supposed to support their claims. Unfortunately, no study results are offered that would illuminate whether there are actually any gender differences in understanding the examples, nor are we told how typical or widespread such examples are in textbooks.

The authors then partially contradict themselves by saying that “many young women do, in fact, have the kind of background needed to understand such problems ab initio.” The upbringing of the daughters of one author and their familiarity with chainsaws and other tools is offered as proof. Then we are told, again without data or references, that “a significant fraction of women, particularly those raised in urban or suburban environments, do not have that background.” The reader is left to wonder how young men would acquire their “special knowledge” in urban or suburban environments.

In our view, the authors draw a conclusion and make recommendations based on anecdotes and stereotypes. Without data on whether textbook problems require prior knowledge that places an asymmetric burden on women, one cannot know if their conclusion is correct. The article is simply a speculative opinion piece.