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Non probability sampling methods do not use random selection techniques, and so are not ideal from a statistical viewpoint. However, they are commonly used in analytic investigations, where the internal validity does not need to be as high as for descriptive studies.
Non probability sampling methods do not use random selection techniques, and so are not ideal from a statistical viewpoint. However, they are commonly used in analytic investigations, where the internal validity does not need to be as high as for descriptive studies.
====Judgement sample====
====Judgement sampling====
In this type of sampling, the study sample is chosen because they are considered by the investigator to be representative of the source population. As such, the criteria for selection (and therefore the definition of the source population) are not stated, making it very difficult to assess the validity of the results obtained. This sampling method is therefore not advised.
====Convenience sample====
====Convenience sampling====
The selection of the study population in these cases is based on convenience - for example, ease of access, availability of data or the presence of a sampling frame. Despite the limitations of this approach, the criteria for selection can often be clearly defined, and an analytic study using convenience sampling may be able to be extrapolated to a larger target population in some cases.
====Purposive sampling====
==Sample size calculation==
==Sample size calculation==