Note: These categories are provided only
for additional information for EPSY 341 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
- Homogeneous - Focuses, reduces variation, simplifies analysis, facilitates group
- 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
- 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
Del Siegle, Ph.D.