# Sex ratio at birth

This article describes a ratio measure. In the standard operationalization, the numerator of the measure is number of male live births (view other ratio measures with this numerator) and the denominator of the measure is number of female live births (view other ratio measures with this denominator). The denominator used for reporting is 100. The measurement period is a variable.

## Definition

The sex ratio at birth (SRB) for a given population over a given time period is the ratio of the number of male live births in the population to the number of female live births to the population, scaled to a denominator of 100, i.e., it is the number of male live births for every 100 female live births.

Note that SRBs may instead be reported as the number of female live births per 100 male live births, so please be careful regarding the reporting convention.

## Refinements

Criterion of refinement Explanation Significance
birth order of the birth, or equivalently, the parity of the mother at the time of birth We can consider the sex ratios at birth restricted to live births that occur at a particular birth order. For instance, the SRB at birth order 1 is the number of male live births of first children for every 100 female live births of first children. Comparing SRBs for different birth orders allows us to estimate the extent of sex-selectivity in conception and abortion.
sex sequence of births for the mother prior to the birth We can consider the sex ratios at birth for specific sex sequences of prior births. For instance, we can consider the sex ratio at births for births to women who have had two male births and no female births. This is also a tool in measuring sex-selectivity in conception and abortion, in relation to the existing family structure.
age of the mother (yielding an age-specific sex ratio at birth) We consider the sex ratio at birth for births to mothers of specific ages. This is useful insofar as it sheds light on the relation between age and sex-selectivity.