Purposive Sampling

A popular method in qualitative research, purposive sampling techniques are used to select subjects on the basis of a particular characteristic.

Combination or Mixed Purposeful - Triangulation, flexibility, meets multiple interests and needs. (Patton, 1990)

Confirming or Disconfirming - Elaborating and deepening initial analysis, seeking exceptions, testing variation.

Convenience - Saves time, money, and effort. Poorest rational; lowest credibility. Yields information-poor cases.

Criterion - Picking all cases that meet some criterion, such as all children abused in a treatment facility. Quality assurance.

Critical Case - Permits logical generalisation and maximum application of information to other cases because if it's true of this once case it's likely to be true of all other cases.

Extreme or Deviant Case - Learning from highly unusual manifestations of the phenomenon of interest, such as outstanding success/notable failures, top of the class/dropouts, exotic events, crises.

Homogeneous - Focuses, reduces variation, simplifies analysis, facilitates group interviewing.

Intensity - Information-rich cases that manifest the phenomenon intensely, but not extremely, such as good students/poor students, above average/below average.

Maximum Variation - Purposefully picking a wide range of variation on dimensions of interest...documents unique or diverse variations that have emerged in adapting to different conditions. Identifies important common patterns that cut across variations.

Opportunistic - Following new leads during fieldwork, taking advantage of the unexpected, flexibility.

Politically Important Cases - Attracts attention to the study (or avoids attracting undesired attention by purposefully eliminating from the sample politically sensitive cases).

Random Purposeful - (still small sample size) Adds credibility to sample when potential purposeful sample is larger than one can handle. Reduces judgment within a purposeful category. (Not for generalizations or representativeness.)

Stratified Purposeful - Illustrates characteristics of particular subgroups of interest; facilitates comparisons.

Snowball or Chain - Identifies cases of interest from people who know people who know people who know what cases are information-rich, that is, good examples for study, good interview subjects.

Theory-Based or Operational Construct - Finding manifestations of a theoretical construct of interest so as to elaborate and examine the construct.

Typical Case - Illustrates or highlights what is typical, normal, average.


Patton, M. Q. (1990). Qualitative evaluation and research methods (2nd ed.). Newbury Park, CA: Sage Publications.

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