In most psychological research, we need a group of participants to study. (There are exceptions to this — some studies are reviews, or involve re-analysis or meta-analysis of previously published data.) When assembling a group of participants, the group of people we are interested in is called the population. The subset of the population you have access to is called the target population — for example, if you are interested in A-level students, you probably just have access to the A-level students at one school or college. There are usually still too many people in the target population to study, so we need a smaller group to work with. This smaller group is called the sample. The way we select the sample is known as the sampling technique. The broad aim of the sampling technique is to select a sample that is representative of the target population.
Generally speaking, there is a trade-off between using either quick and easy sampling techniques, or using more complicated and time-consuming ones that will produce a more representative sample. Sometimes it is critical to end up with a very representative sample, other times not so much. For example, if you are interested in political opinions, then a representative sample is critical because such opinions will vary massively according to age, social class, region, intelligence and personality. Therefore, if you want to really understand political opinions across a country you need a sample that represents all those differences. On the other hand, if you are interested in memory, a representative sample is less critical — memory doesn’t particularly vary by demographics (with the possible exception of age). Some sampling techniques are described below.
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