Judgment sampling (a type of purposive sampling) occurs when units are selected for inclusion in a study based on the professional judgment of the researcher. This is in contrast to probability sampling techniques in which units are drawn with some probability (e.g., randomly) from the population of interest. This entry describes the common forms of judgment sampling and discusses their advantages and limitations.

Judgment sampling may be used for a variety of reasons. In general, the goal of judgment sampling is to deliberately select units (e.g., individual people, events, objects) that are best suited to enable researchers to address their research questions. This is often done when the population of interest is very small, or desired characteristics of units are very rare, making probabilistic sampling infeasible. ...