Sampling interval

A sampling interval is the distance or step between units selected from a population in a research study. It is commonly used in systematic sampling, also called 'nth selection', where every nth unit from a list is chosen to form the sample.

For example, if a population contains 10,000 individuals and a sample of 2,000 is required, the sampling interval would be five, meaning every 5th person on the list is selected. The starting point can be random – such as the 1st, 6th, 11th unit, or the 3rd, 8th, 13th unit – ensuring that the selection is spread evenly throughout the population.

Using a sampling interval is a randomised technique that helps create a sample that is more likely to be representative of the total target population than purely non-random methods. This, in turn, increases the reliability of conclusions drawn from the research data.

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