Update. This qualification applies to all the studies I've collected in this thread: "Different research does not understand the concepts of 'man/woman' and 'male/female' in the same way, and there is no discussion nor written consensus on how to tackle these issues ethically and correctly within #Bibliometrics."
digibug.ugr.es/bitstream/handl…

Another qualification: Most of these studies determine the sex/gender of authors by using software that makes guesses based on their names.

#Gender