Understanding Purposive Sampling

A purposive sample is a non-probability sample that is selected based on characteristics of a population and the objective of the study. Purposive sampling is different from convenience sampling and is also known as judgmental, selective, or subjective sampling.

This type of sampling can be very useful in situations when you need to reach a targeted sample quickly, and where sampling for proportionality is not the main concern. There are seven types of purposive samples, each appropriate to a different research objective.

Types of Purposive Samples

Maximum Variation/Heterogeneous

A maximum variation/heterogeneous purposive sample is one which is selected to provide a diverse range of cases relevant to a particular phenomenon or event. The purpose of this kind of sample design is to provide as much insight as possible into the event or phenomenon under examination. For example, when conducting a street poll about an issue, a researcher would want to ensure that he or she speaks with as many different kinds of people as possible in order to construct a robust view of the issue from the public's perspective.

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Homogeneous

A homogeneous purposive sample is one that is selected for having a shared characteristic or set of characteristics. For example, a team of researchers wanted to understand what the significance of white skin—whiteness—means to white people, so they asked white people about this. This is a homogenous sample created on the basis of race.

Typical Case Sampling

Typical case sampling is a type of purposive sampling useful when a researcher wants to study a phenomenon or trend as it relates to what are considered "typical" or "average" members of the effected population. If a researcher wants to study how a type of educational curriculum affects the average student, then they choose to focus on average members of a student population.

Extreme/Deviant Case Sampling

Conversely, extreme/deviant case sampling is used when a researcher wants to study the outliers that diverge from the norm as regards a particular phenomenon, issue, or trend. By studying the deviant cases, researchers can often gain a better understanding of the more regular patterns of behavior. If a researcher wanted to understand the relationship between study habits and high academic achievement, they should purposively sample students considered high achievers.

Critical Case Sampling

Critical case sampling is a type of purposive sampling in which just one case is chosen for study because the researcher expects that studying it will reveal insights that can be applied to other like cases. When sociologist C.J. Pascoe wanted to study sexuality and gender identity develop among high school students, she selected what was considered to be an average high school in terms of population and family income, so that her findings from this case could be more generally applicable.

Total Population Sampling

With total population sampling a researcher chooses to examine the entire population that has one or more shared characteristics. This kind of purposive sampling technique is commonly used to generate reviews of events or experiences, which is to say, it is common to studies of particular groups within larger populations.

Expert Sampling

Expert sampling is a form of purposive sampling used when research requires one to capture knowledge rooted in a particular form of expertise. It is common to use this form of purposive sampling technique in the early stages of a research process, when the researcher is seeking to become better informed about the topic at hand before embarking on a study. Doing this kind of early-stage expert-based research can shape research questions and research design in important ways.

Updated by Nicki Lisa Cole, Ph.D.