Three elements are used to determine the sample size:

1. The margin of error.

2. The level of confidence.

3. The variance of the universe or population.

They must be joined by the size of the universe, because it is in relation to that measure that we will establish the representativeness of the sample. Usually it is recommended to distinguish between finite populations and infinite populations. The former are those in which there are less than 500,000 units or individuals, while the latter are those that exceed that number. A different formula is used for each of them.