As in field epidemiology we often need to study the relationship between diseases and their determinants in a population, we may face a problem when the population is very large. It may not be possible, nor desirable, to include each individual in the population in the study. As an alternative, we would like to perform the study in a smaller group, that represents the study population in all relevant aspects of disease occurrence and distribution of determinants. This will allow us to achieve the same study objectives with the same validity at lower costs and reduced field time.

The identification and selection of such a representative smaller population is known as sampling.

Practical definition

Sampling is the procedure by which some members of a given population are selected as representatives of the entire population in terms of the desired characteristics.

Learning objectives

After reading the pages linked to this chapter, you should be able to better understand:

• Why we use sampling
• Representativity, validity, precision and generalizibility of samples
• Some concepts in sampling, including
  • Selecting different units of sampling
  • Determine the sampling fraction
  • Select the sampling frame
  • Design a sampling scheme
• Sampling errors