Purposive Sampling

Purposive sampling in qualitative inquiry is the deliberate seeking out of participants with particular characteristics, according to the needs of the developing analysis and emerging theory. Because, at the beginning of the study, the researcher does not know enough about a particular phenomenon, the nature of the sample is not always predetermined. Often, midway through data analysis, the researcher will realize that he or she will need to interview participants who were not envisioned as pertinent for the study at the beginning of the project. For example, Martin (1998), in her study of sudden infant death syndrome (SIDS), discovered issues of control over the responsibility for these infants between the groups of first responders (emergency medical technicians and the firefighters) and realized that she would have to interview these professionals, extending her study beyond the interviews with parents, as originally perceived.

Types of purposive sampling are nominated or snowball sampling (in which participants are referred by members of the same group who have already been enrolled in the study) and theoretical sampling (in which participants are deliberately sought according to information required by the analysis as the study progresses).

In nominated or snowball sampling, the researcher locates a “good” participant and, at the end of the interview, asks the participant to help with the study [Page 885]by referring the researcher to another person who may like to participate in the study. Thus, sampling follows a social network. Nominated or snowball sampling is particularly useful when groups are hard to identify or may not volunteer or respond to a notice advertising for participants. It is a useful strategy when locating participants who would otherwise be hard to locate, perhaps because of shame of fear of reprisal for illegal activities, such as drug use; a closed group, such as a motorcycle gang; or those who have private behaviors or a stigma associated with a disease. Gaining trust with the first participant and allowing that person to assure the group that the research is “OK” provides access to participants who would otherwise be unobtainable.

The final use of a nominated sample is by researchers who are using theoretical sampling. They may use a form of nominated sample by requesting recommendations from the group for participants who have certain kind of experiences or knowledge needed to move the analysis forward.