Although it is often true that the association between two variables may be due to some unobserved third variable, the plausiblity of such arguments needs careful examination. In 1987, a Canadian court accepted an explanation offered by the National Revenue Service of Canada that, in a test for promotion, lower pass rates among women than among men were explained by differences in rates of college attendance, a variable that was not directly observed by the court. We show that this explanation is not merely implausible. It is impossible. We conclude with a brief discussion of the role of a statistician in an argument involving an unobserved variable.