Summary

In this study session you have learned that:

1. Sampling is a process of selecting study subjects from a defined population.
2. To generalise results from a sample to a whole study population it is necessary for the sample to be representative.
3. Representativeness of a sample can be ensured by using probability sampling methods. This uses random selection of study subjects and ensures an equal chance (or probability) of any subject being selected in the sample for the research study.
4. Commonly used probability sampling methods are simple random sampling, systematic random sampling and stratified random sampling.
5. Non-probability sampling methods are used to select a sample of study subjects for qualitative research into their knowledge, attitudes and practices. This method uses some form of selection criteria and the results cannot be generalised to the population as a whole.
6. If a sampling method includes all of the population within a defined boundary it is called a census and the sampling method is called census sampling.
7. In determining the appropriate sample size for a research study you should consider whether you need to be able to generalise from the findings and what type of data you plan to collect. The sample size must be large enough to be representative of the population as a whole if the research is quantitative and the sample has been chosen using a probability sampling method. The sample size is not relevant if the research is qualitative and the sample has been chosen by a non-probability sampling method.