When you conduct research about a group of people, it’s rarely possible to collect data from every person in that group. Instead, you select a sample. A sample is a group of individuals who will actually participate in the research. To draw valid conclusions from your results, you have to carefully decide how you will select a sample that is representative of the group as a whole.
There are two types of sampling methods:
- Probability sampling involves random selection, allowing you to make statistical inferences about the whole group.
- Non-probability sampling involves non-random selection based on convenience or other criteria, allowing you to easily collect initial data.
Population vs sample
The population is the entire group that you want to draw conclusions about. The sample is the specific group of individuals that you will collect data from. The population can be defined in terms of geographical location, age, income, and many other characteristics.
Probability sampling methods
Probability sampling means that every member of the population has a chance of being selected. If you want to produce results that are representative of the whole population, you need to use a probability sampling technique.
- Simple random sampling.
- Systematic sampling. ...
- Stratified sampling. ...
- Clustered sampling. ...
In this case, each individual is chosen entirely by chance and each member of the population has an equal chance, or probability, of being selected. ...
Non-probability sampling methods
In a non-probability sample, individuals are selected based on non-random criteria, and not every individual has a chance of being included. This type of sample is easier and cheaper to access, but you can’t use it to make valid statistical inferences about the whole population.
Non-probability sampling techniques are often appropriate for exploratory and qualitative research. In these types of research, the aim is not to test a hypothesis about a broad population, but to develop an initial understanding of a small or under-researched population.
- Convenience sampling. ...
- Quota sampling. ...
- Judgement (or Purposive) Sampling. ...
- Snowball sampling.
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