Ratios
Ratios are another way of describing the structure of a population. However, rather than describing the size of a sub-group relative to the total population, ratios describe the size of a sub-group relative to another sub-group. The numerator is not included in the denominator.
The most commonly used ratio in demography is the sex ratio, which describes the number of men relative to the number of women (i.e. number of men divided by the number of women). This can be done for the whole population, but is more commonly calculated for specific age groups. This will be described in greater detail later in this session. Other commonly used ratios include dependency ratios and the child-woman ratio.
| ratio = | P1 |
| P2 |
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to see an example.
In France in 2001 there were 770,945 births. Of these, 394,297 were male and 376,648 were female. From this information, the sex ratio at birth (SRAB) can be calculated as follows.
| SRAB = | 394297 | = 1.047 |
| 376648 |
Therefore the SRAB is 1.047. We could also express this as the number of male births for every 100 female births by multiplying the total by 100. So for every 100 girls born, there were 105 boys born.