The Williams Institute of the UCLA Law School published a paper titled Best Practices for Asking Questions to Identify Transgender and Other Gender Minority Respondents on Population-Based Surveys. It's a culmination of studies by the Gender Identity in U.S. Surveillance (GenIUSS) group about the best way to accurately identify transgender people and other gender minorities in surveys.
They recommend that when two questions can be included they be asked as:
ASSIGNED SEX AT BIRTH
What sex were you assigned at birth, on your original birth certificate?
CURRENT GENDER IDENTITY
How do you describe yourself? (check one)
- Do not identify as female, male, or transgender
(They're also exploring a further breakdown of the responses for the Current Gender Identity question using the options "male," "female," "trans male/trans man," "trans female/trans woman," "genderqueer/gender non-conforming," and "different identity (please state): _______")
When only a single question can be included in a response form, the report recommends phrasing it as
Some people describe themselves as transgender when they experience a different gender identity from their sex at birth. For example, a
person born into a male body, but who feels female or lives as a
woman. Do you consider yourself to be transgender?
- Yes, transgender, male to female
- Yes, transgender, female to male
- Yes, transgender, gender non-conforming
The paper also includes a recommended way of asking about LGBT identity:
Do you think of yourself as (please check all that apply):
- Gay or lesbian
- Transgender, transsexual, or gender non-conforming
IF yes to transgender, then probe:
- transgender or transsexual, male to female
- transgender or transsexual, female to male
- Gender non-conforming
The paper also provides some recommendations on collecting this data from adolescents, ethnic minorities, and low socio-economic status communities.