Purposeful Sampling

Sixteen Types of Purposeful Sampling for Qualitative Research

Did you know that there are 16 types of purposeful sampling (Patton, 1990)? Before starting your next research project, take a peek at these various sampling methods to determine which is best for your study.

  1.  Intensity: This method selects excellent examples of the phenomenon of interest (but not extreme examples), and allows the researcher to select a small number of cases—but it requires prior knowledge to know what to look for.
  2. Maximum Variation: This type of sampling purposely incorporates participants that exhibit wide variability on the phenomenon of interest, which allows for investigation of variables across a variety of people and situations.
  3. Homogenous:  This selects a small, homogenous group of participants. This is useful for investigating a group or groups in depth.
  4. Typical Case: This is exactly what it sounds like: a sample is drawn from a group that is considered typical (average) for your variables of interest. This is useful for understanding phenomena in ordinary situations.
  5. Stratified Purposeful: For this method, samples are drawn from subgroups. For example, if you wanted to sample university students you could stratify the sample by class and then select the appropriate number of sophomores, freshmen, juniors, and seniors (Babbie, 2007). This method results in a more credible study that is representative of your population of interest.
  6. Critical Case: Selects cases that are most likely to result in the most information, or have the greatest impact. This is useful when funds are limited, but generalizability is limited.
  7. Snowball/ Chain: This method capitalizes on relationships. For example, this method may be used to find doctoral candidates. You first identify your first participant, who refers you to doctoral candidates that they know, who then refer you to candidate that they know, and so on. This is useful to identify a small number of key cases. 
  8. Criterion: For this method, the researcher sets some criteria (i.e., students in 3rd grade). This is useful to investigate phenomena in a specific set of people.
  9. Theory Based/ Operational Construct: Choosing a sample based on theory. This is useful when the research focuses on theory, and researchers want to know how the theory manifests in this group.
  10. Confirming and Disconfirming Cases: This sample selection actually occurs after some data have been collected and involves the identification of cases in support of, or against, the phenomena of interest. This creates a better understanding of the phenomena. 
  11. Opportunistic: Opportunistic sampling takes advantage of events as they unfold (i.e., sampling witnesses to some national event). This is useful in exploratory research settings. 
  12. Random Purposeful: This sampling takes a random subset of participants from a population of interest, and lends credibility to a study. 
  13. Sampling Politically Important Cases: This involves sampling from a politically sensitive site, which may draw attention to the research and its findings—which increases the study’s impact. 
  14. Convenience: This is exactly what it sounds like: obtaining a sample that is easy to find. On college campuses, a convenience sample would be college undergraduates. 
  15. Combination/ Mixed Purposeful: This method combines one or more sampling techniques discussed above to allow for the best sample possible.   
  16. Random: Used for experimental and quasi- experimental designs when researchers want to generalize their results to a bigger population.

 For more info:

Babbie, E. (2010). The Practice of Social Research (13th Ed.). Belmont, CA: Thomson Wadsworth Publishing.

Cohen, D., & Crabtree, B. (2006, July). Qualitative Research Guidelines Project. Retrieved from http://qualres.org/index.html

Patton, M. Q. (2002). Qualitative Research and Evaluation Methods (3rd Ed.). Thousand Oaks, CA: Sage Publications.