## Calculating numbers in the target population

The table below shows an estimate of the target population for immunization in a area with a total population of 5,000. A figure of 4% of the population is has been taken to estimate the coverage required for all live births and surviving infants (this figure will vary from country to country). We will assume that (on average) about 23% of the population will be women of childbearing age, of whom about 4% will be pregnant in a typical year.

## Estimating the target population (pt) for immunization in a area with a total population of 5,000.

Category% of total populationEstimated number in target population
Live births 3.6 180
Surviving infants 3.4 170
Women of childbearing age (pregnant and non-pregnant) 23 1,150

You estimate the target population by multiplying the total population by the percentage in a particular category; for example in the table above:

Expressing a percentage as a decimal number is easy, e.g. 90% is the same as 0.9; 23% is the same as 0.23, and 4% is the same as 0.04.

• The estimated number of women eligible for TT vaccination is 5,000 x 23% (or 0.23) = 1,150
• The estimated number of children eligible for all other EPI vaccines is 5,000 x 4% (or 0.04) = 200, if you take the simple average of 4%.
About 23% of the Ethiopian population are women of childbearing age (pregnant and non-pregnant combined). (Photo: Ali Wyllie)