So, are you male or female? If you take part in a typical study in my area of language of cognitive sciences, you got to be one or the other. This is simply the way studies are designed. I have never seen an exception.
We tend to think of gender as a matter of various appendages. In that sense I'd wager that most researchers are not aware of how problematic this question is, even while we are aware that for some, checking the anatomy doesn't work. There is no agreement on for how many this is the case - my vague summary of different estimates is "one in thousands". Numbers are clearer when we consider gender as identity: Official UK statistics speak of one in about 250 who consider themselves neither male nor female.
Over my career I must have tested, or supervised the testing, of around 1000 people. This means that when I gave participants the option of labeling themselves male or female, or when I simply ticked the box for them based on their appearance, I assigned a label to a handful of people for whom the distinction does not work.
One could say that identity should not be what matters. After all, in my field language is treated as a biological phenomenon. However, identity is certainly a property of the brain and therefore closer to what matters in my field than the bits and pieces by which we assign gender in the anatomic sense.
One could also argue that even if the participant's sex has an effect on language processing (in most cases, we find no differences), a number like one in 250 is low enough to call the whole issue a small measurement error (and be right about it, as cynical as this sounds). If I wrongly categorize one participant in a study with 250 subjects, my overall results are not going to change.
But this is not a matter of correct measurement, but of letting participants know that they are represented. Non-binary individuals have higher risk of depression and suicide, associated with difficulties getting others to accept their identity. By offering more than two options when asking about gender, we show a non-binary person that a gender that is neither male nor female will not be simply ignored. We also make all participants, regardless of gender, aware of the issue.
It took me until last year to realize this.
I had secured some tiny funding for a research activity at 2016's Bloomsbury Festival, for a day in which the public could talk to researchers and take part in a short experiment. Our group, consisting of me and a few colleagues (mostly PhD students) had a few aims. Most importantly, we wanted to introduce our research in a fun way, and make people think about their language system. We also wanted to keep the data for a potential publication, which meant that we had to apply to ethical approval and, of course, ask the gender question. With our activity at the festival we were representing UCL. We wanted to present it as an open, socially progressive place, especially in a year which had been so difficult for people with a progressive cause. It quickly became clear that the usual binary question would not cut it.
But what is the right question? I had a number of problems. The first is that we were working on the research activity in addition to our usual work. We were busy enough getting the activity to work, and I did not have much time to do deep research on how to ask about gender in an includive way. The other problem is that I am not in touch with LGBTQ issues. Wanting to be inclusive is one thing, nailing the language the other, especially considering how quickly gender terms can change, lose or gain connotations.
I turned to Facebook, where I am in contact with dozens of researchers. Not only did no one make any suggestions - no one replied. On the Internet I found dozens of proposed solutions. I found some very confusing. For example, the website It's Pronounced Metrosexual makes one suggestion which contains 17 options (Man, Woman, Transgender, Transsexual, Genderqueer, Genderfuck, Non-gendered, Agender, Genderless, Non-binary, Trans Man, Trans Woman, Third Gender, Two-Spirit, Bi-Gender, Genderfluid, Transvestite). This is the sort of list some conservatives would show to mock the entire effort.
I turned to two gay colleagues in the festival group. I thought they might be more involved with questions about gender identity, and was relieved when I found that this was the case. By that time I favoured a solution with three options: Male, Female and Trans*, with the latter standing for all kinds of trans groups. They told me Trans* wasn't a great idea. Especially trans men and women don't want to be considered trans - they want to be simply male or female according to their identity. One of the colleagues asked some friends and acquaintances, and as a result we ended up with Female, Male and Non-binary.
On the day of the festival about 150 people took part in our activity. While everyone was given the three options, no one raised the "new" gender question to us, let alone complained about it. One visitor selected "Non-binary". As I explained above, we did not do it for this one person, but to go one step towards better inclusivity overall. I am keen to stick to these three options in future research studies.