Referenced by 16 other explainers
Sex is a core way to split a population. People are grouped as female or male at every age. Projections use three main axes: sex, age, and year. Of these, sex is the best recorded. Errors are rare and coverage is high.
Sex is recorded at birth, based on the sex characteristics seen at the time. State and territory offices log it in their Births, Deaths and Marriages books. The ABS rolls these records up to national birth and death counts. The Census also records sex. The Estimated Resident Population uses these sources to estimate the population by sex and age. Life tables are built by sex and age.
A few more males are born than females. The sex ratio at birth sits near 105 male births per 100 female births. This ratio is steady and does not vary much by place or year. Every cohort-component method rests on it. The model works out total births first, then splits them by sex using this ratio.
Mortality rates differ by sex and age. At most ages, males have higher mortality rates than females. The gap is largest in young adult and late working ages. At very old ages there is a crossover: more females than males are still alive, even though more males were born in each cohort. Because the death pattern differs, life tables are built by sex. Place Forecast uses one life table for females and one for males.
Fertility rates are worked out for females of child-bearing age. This is because births are most directly linked to the female population at risk. This setup is called female-dominant. Rates can also be calculated for males, but male-based and female-based results do not always line up. This difference is known as the two-sex problem. To avoid this problem, the ABS, Place Forecast, and most projection systems use female fertility rates only.
Migration patterns differ by sex too. Student flows skew one way at some ages, work visas another, and partnering moves another again. Past waves of Australian migration were often male-heavy, such as the post-war work programs. Projections split migration by sex and age.
Sex and gender are not the same. Sex is recorded at birth and in the Census. Gender is a personal identity and may or may not match it. A person's reported sex can change over time. It may differ from the sex recorded at birth. The ABS set a new standard in 2020 that treats them as two separate items. The 2021 Census asked sex, with a write-in for those outside female or male. A gender question is planned for the 2026 Census. Place Forecast is binary because its ABS inputs are binary, not by choice.
Place Forecast splits every count and rate by female and male. This matches every ABS input we use. Fertility rates apply to females of child-bearing age only, in line with the female-dominant answer to the two-sex problem. Mortality rates use sex-specific life tables. Migration flows are split by sex and age. The sex ratio at birth sets how projected births are split into female and male. Female is listed before male in every table, chart, and filter.