This indicator corresponds to the ratio between the number of men and the number of women in a population. It is expressed as the number of men per 100 women. A value less than 100 means that there are more women than men, and vice versa.

At birth, the sex ratio is 105 boys for every 100 girls. Since the death rate of boys is generally higher than that of girls, the ratio decreases with age, and adult women are the majority. At an advanced age, this ratio decreases given the longer life expectancy of women.

The sex ratio is therefore largely dependent on the age structure of the population. The older a population, the more likely it is to have a low sex ratio, with more women than men. However, we can see that the difference in life expectancy between men and women is shrinking every year. Therefore, the impact of age structure on the sex ratio is also reduced: in some cases, the population is aging and the relative number of men is increasing at the same time.

However, this is not the only factor that determines the numerical ratio between men and women. Divergent migration paths by sex and age also have an influence on the sex ratio.