I'm surprised that in the BSRI male students and female students score so similarly. Did the researchers decide which answers would be masculine or feminine a priori, rather than a posteriori?

Wikipedia describes its origin. The items on the test are based on the opinions of 100 Stanford undergraduates in the 1970s about what traits of behaviour and personality in each sex are socially desirable, and the norming of the test was done with a total of about 1500 Stanford undergraduates.

Here is a review article about the BSRI from 2001.