Sampling is the process of selecting a smaller group of people from a larger population to take part in your research. The sampling method you choose affects how representative your results are and how confidently you can apply your findings to the wider population.
There are two main types of sampling methods:
Probability sampling – every member of the population has a known chance of being selected.
Non-probability sampling – the chances of selection are unknown.
Examples of probability sampling methods
Simple random sampling. Simple random sampling means that every member of the target population has an equal chance to be selected for the study. In other words, respondents are chosen completely at random.
Stratified random sampling. In stratified samples, the population is divided into groups, based on certain characteristics (e.g., age and gender). Within each group, a probability sample (often a simple random sample) is selected. In stratified sampling, the groups are called strata.
Systematic random sampling. When using this sampling method, a list containing every member in the population of interest is created. From this list, the first x elements are chosen. Thereafter, every xth element in the list is chosen. Note that this sampling method differs from simple random sampling in that not every element in the population is equally likely to be selected for the sample.
Examples of non-probability sampling methods
Convenience Sampling. Convenience sampling means collecting a sample of whichever participants are easiest to reach. It’s a first come, first serve sample.
Quota Sampling. This method is similar to stratified sampling: the population is divided into groups, based on certain characteristics. Within each group, a non-probabilistic sample (often a convenience sample) is selected.
Purposive Sampling. In this sampling method, individuals are hand-selected to be part of a sample. This might be because the individual's views are considered to be particularly important or representative of the population under investigation.