From gender-fluid and non-binary to genderqueer, the world has grappled in recent years with the growing spectrum of how people identify themselves.

Now an Australian study has found more than 30 separate gender definitions available on social media platforms or offered by government institutions.

These include "pangender", "poligender", "transgender", "androgyne" and "demigirl" alongside the traditional male and female.

The research, based on Queensland University of Technology's Australian Sex Survey, found women had more choice than men, according its author Stephen Whyte.

"While gender can no doubt be a complex issue for males, our research showed just how many factors can influence a female's decision, including reproductive pressure, labour market inequality and disproportionate levels of education," he said.

Even height could be a defining factor, "with taller females more likely to identify as non-binary", Whyte said in a press release.

Most older respondents opted for the binary definitions of male and female.

Questions of gender self-identification have split public opinion around the world.

In the United States, the election of Donald Trump as president ended debate begun under the previous Obama administration over whether to add a gender identity question to the national census.

Many young people state their "preferred pronouns" on social media, with some opting for the gender neutral "they/them".

According to the World Health Organisation, gender "refers to the socially constructed characteristics of women and men – such as norms, roles and relationships of and between groups of women and men".