Judgment sampling is a method in statistics and quantitative research for non-randomly selecting subjects for study from a population by selecting according to the opinion of an expert. It is a biased method that is useful when some members of a population make better subjects than others. The nature of judgment sampling makes data derived by this method harder to generalize and prone to an increased chance of misrepresentation.
In judgment sampling, an expert hand-picks units for study according to their perceived usefulness to the research. This method is in contrast to random sampling, in which each member of a population has a known, non-zero chance of being selected as part of the sample.
For example, when interviewing manufacturers in the pharmaceutical industry to determine their preferred brand of equipment, the schedules, availability and willingness of the possible subjects are taken into account. Rather than performing random sampling and selecting subjects who are unavailable, an expert employs judgment sampling and selects units whose availability and attitude are compatible with the study.
Judgment sampling is useful when a limited number of individuals possess the trait of interest. The drawback of judgment sampling is that it is prone to bias. There is no definitive way to prove the reliability of the expert who selects the sample. Moreover, the lack of randomization and the fact that members of the population do not have equal chances of being selected may result in misrepresentation of data.