There has long been greater complexity in the area of gender identity than the male-female binary distinction would suggest.
This paper provided the basis for an in-depth review of measuring gender identity conducted by the Bureau of the Conference of European Statisticians (CES) in February 2019.
It summarizes the main needs for statistical measurement of gender identity, the challenges posed, and the variety of approaches so far taken. It gives a detailed overview of current practice in those countries leading the efforts to begin measuring gender identity and presents an annex of country practices and situations in CES countries and beyond.