Purposive Sampling

Note: These categories are provided only for additional information for EPSY 5601 students.

PURPOSIVE SAMPLING – Subjects are selected because of some characteristic. Patton (1990) has proposed the following cases of purposive sampling. Purposive sampling is popular in qualitative research.

  • 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.
  • 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.
  • Homogeneous – Focuses, reduces variation, simplifies analysis, facilitates group interviewing.
  • Typical Case – Illustrates or highlights what is typical, normal, average.
  • Stratified Purposeful – Illustrates characteristics of particular subgroups of interest; facilitates comparisons.
  • Critical Case – Permits logical generalization 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.
  • 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.
  • Criterion – Picking all cases that meet some criterion, such as all children abused in a treatment facility. Quality assurance.
  • Theory-Based or Operational Construct – Finding manifestations of a theoretical construct of interest so as to elaborate and examine the construct.
  • Confirming or Disconfirming – Elaborating and deepening initial analysis, seeking exceptions, testing variation.
  • Opportunistic – Following new leads during fieldwork, taking advantage of the unexpected, flexibility.
  • 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.)
  • Politically Important Cases – Attracts attention to the study (or avoids attracting undesired attention by purposefully eliminating from the sample politically sensitive cases).
  • Convenience – Saves time, money, and effort. Poorest rational; lowest credibility. Yields information-poor cases.
  • Combination or Mixed Purposeful – Triangulation, flexibility, meets multiple interests and needs. (Patton, 1990)

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

Del Siegle, Ph.D.