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Sometimes a select group of people will be surveyed. Unlike convenience samples, purposeful samples are carefully selected to achieve a specific objective.
Purposeful sampling selects information-rich cases for in depth study. Size and specific cases depend on the study purpose. There are different types of purposeful sampling. They are briefly described below for you to be aware of them. The details can be found in Patton (1990).
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Typical case sampling
Taking a sample of a typical, normal or average example for a particular phenomenon/subject. |
Theory based or operational construct sampling
Finding manifestations of a theoretical construct of interest so as to elaborate and examine the construct. |
Confirming and disconfirming cases
Seeking information that either confirms a hypothesis or disconfirms it. This type of sampling includes seeking exceptions and testing variation. |
Maximum variation sampling
This involves purposefully picking the widest possible range of experiences or views. Maximum variation sampling documents unique or diverse variations that have emerged in adapting to different conditions. It also identifies important common patterns that cut across variations.
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Snowball or chain sampling
Snowball or chain sampling involves asking each participant to identify others who might be helpful in completing the study. This approach to sampling is particularly helpful in gaining access to closed groups such as insular religious orders, drug addicts or homeless populations. |
Criterion sampling
Here, you set a criteria and pick all cases that meet that criteria for example, all ladies six feet tall, all white cars, all farmers that have planted onions. |
Extreme and deviant case sampling
This involves learning from highly unusual manifestations of the phenomenon of interest, such as outstanding successes, notable failures, top of the class, dropouts, exotic events, crises. |
