Nonprobability sampling is a type of sampling, where members of sample are not chosen randomly. Unlike probability sampling, all members of population do not have an equal chance of being selected for the study. As a result, the obtained results of such studies cannot be generalized to the members of target population. In general, Nonprobability sampling is implemented in two ways, namely convenience sampling and purposive sampling. Convenience sampling is a nonprobability sampling, where samples are selected based on their availability and ease of access. On the other hand, in purposive sampling the samples are selected based on the judgment of the researchers.
Different types of purposive sampling include:
Modal instance sampling: The term “mode” in statistics refers to the most frequently occurring number. Therefore, in this type of sampling, the researcher looks for the most frequent or the typical member of a population. This technique is used for investigating common beliefs of a society.
Expert sampling: This technique is used where the samples are drawn from the experts in the field. The main purposes of this type of sampling include having access to the experts’ opinions and also validating other sampling methods.
Quota sampling: This type of sampling is similar to probability stratified sampling. In this regard, the researcher categorizes the population into groups and then selects the samples from the categorized groups.
Judgmental sampling: Judgmental sampling is a non-probability sampling technique, where population is divided into groups based the researcher’s knowledge and judgment and then the convenience sampling is implemented.
Snowball sampling: In this type of sampling, the researcher asks the intended participants to recruit other participants. This technique is suitable to study inaccessible population, such as addicted individuals.
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