Non-Probability Sampling


non-probability sample is a sample that relies on personal judgment somewhere in the element selection process and therefore prohibits estimating the probability that any population element will be included in the sample.

convenience sample is a non-probability sample that is sometimes called an accidental sample because those included in the sample enter by accident in that they just happen to be where the study is being conducted when it is being conducted.

judgment sample (often called a purposive, selective or subjective sample) is a non-probability sample in which the sample elements are handpicked because they are expected to serve the research purpose. A disadvantage is that it is often prone to researcher bias.

snowball sample is a judgment sample that relies on the researcher’s ability to locate an initial set of respondents with the desired characteristics. These individuals are then used to identify still others with the desired characteristics.

quota sample is a non-probability sample that is selected to represent the proportion of individuals in the overall population with respect to certain characteristics

sequential sample is a non-probability sample formed on the basis of a series of successive decisions. If the evidence is not conclusive after a small sample is taken, more observations are taken; if still inconclusive after these additional observations, still more observations are taken. At each stage, a decision is made as to whether more information should be collected or whether the evidence is sufficient to draw a conclusion.

See Also

Sample representativeness
Probability sampling


  1. American Marketing Association, AMA Dictionary.

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