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Judgment Sampling
A non-probability sampling method in which units are deliberately hand-picked by a researcher based on expert judgment about which units will be most informative or representative, rather than chosen through any randomization procedure.
In Plain English
Judgment sampling, also called purposive sampling, is when a researcher deliberately picks specific units because they believe those units are especially informative, typical, or important, choosing three 'representative' factories to study out of a hundred, or interviewing a handful of recognized subject-matter experts. Unlike convenience sampling, which is driven by ease of access, judgment sampling is driven by expertise and deliberate reasoning about which cases matter most, this can be genuinely valuable when the researcher's judgment is well-informed, but it also means the results depend entirely on the quality of that judgment, and can't be extended to a broader population using standard sampling-error formulas.
Definition
Judgment sampling (also called purposive sampling) selects units deliberately, based on a researcher's expert assessment of which specific units will best serve the study's purpose, whether by being especially typical, especially extreme, especially information-rich, or otherwise strategically chosen, rather than through any random selection mechanism. Because selection is driven entirely by subjective expert judgment rather than a known, quantifiable probability rule, judgment sampling is a non-probability method, and any claims of representativeness rest entirely on the validity of the underlying expert judgment rather than on a statistically verifiable design; it is nonetheless widely and appropriately used in qualitative research, case study methodology, and situations, such as selecting a small number of pilot sites or key informants, where the research question specifically calls for deliberately chosen, information-rich cases rather than a statistically representative cross-section.
Properties
- Judgment sampling differs fundamentally from convenience sampling in its selection logic even though both are non-probability methods, convenience sampling selects on accessibility, judgment sampling selects on the researcher's deliberate assessment of which units are most relevant or informative, the two are frequently confused but rest on different justifications.
- The validity of any conclusions drawn from a judgment sample rests entirely on the expertise, objectivity, and transparency of the selection reasoning, since there is no statistical procedure to independently verify representativeness, well-conducted judgment sampling studies typically document their selection criteria explicitly so readers can evaluate the reasoning themselves.
- Judgment sampling is often the deliberate, appropriate choice, rather than a compromise, in research designs that specifically want depth over breadth, selecting a small number of maximally information-rich or extreme cases (a common strategy in qualitative case study research) is a purposeful use of judgment sampling, not a lesser substitute for a probability sample.
At a Glance