No absolute certainties required; quite to the contrary. The point is that in the vast majority of all scientific studies where subjects are classified as male or female, self reporting of those subjects sex is deemed the most parsimonious method for determining said sex.
So, rather than trying (and likely failing as so many researchers and theoreticians have failed) to find a sex litmus test to determine whether or not Chelsea Manning is, ahem, ‘for reals female’ to test your assumption that she is not, I propose that self reporting be the methodology we stick to.
