1.2 Sampling terminology

How can we determine what constitutes an ‘appropriate’ sample? It is helpful to introduce some terminology as we go through the steps in selecting a sample.

Figure 1 From populations to samples.

First, we need to identify the population in which we are interested – this is known as the ‘target (reference) population’. Then we need to identify how we can choose a sample that is representative of the target population. There are three stages of defining the sample:

Activity 2: Understanding sampling

Timing: Allow about 5 minutes

Can you think of a population you are familiar with or interested in? (If not, try this example: imagine you have access to data on patients presenting to primary healthcare facilities with symptoms of urinary tract infections in the state, province or region where you work.)

Use the space below to answer the following questions:

  • Can you identify the target population?
  • Now think about the source population you might select. Can you imagine a possible study sample for this source population?
  • Finally, note the possible sampling unit.
To use this interactive functionality a free OU account is required. Sign in or register.
Interactive feature not available in single page view (see it in standard view).

Discussion

How did you do with this activity?

If you chose to use the example provided, you might have identified that the target population could be all patients presenting to primary healthcare facilities with symptoms of urinary tract infections in your country. Your source population could be patients in your state or province. For your study sample, you may select a number of primary healthcare facilities from the chosen state or province (for example, 30 facilities), and then select all individual patients who present with symptoms of urinary tract infection. The sampling unit is likely to be an individual patient.

1.1 Why do we need to sample?

1.3 Sampling and validity