PURPOSIVE OR JUDGMENT SAMPLING
In purposive sampling, you decide the purpose you want informants (or communities) to serve, and you go out to find some. This is somewhat like quota sampling, except that there is no overall sampling design that tells you how many of each type of informant you need for a study. You take what you can get.
I used purposive sampling in my study of the Kalymnian (Greek) sponge-fishing industry (1987). I knew I had to interview sponge merchants, boat owners, and divers, but my first interviews taught me that I had to interview people whom I had never considered: men who used to be divers but who had quit, gone to Australia as labor migrants, and returned to the island. It was very easy to find those returned migrants: Everyone on Kalymnos either had one in their family or knew people who did.
There are many good reasons for using purposive samples. They are used widely in (1) pilot studies, (2) intensive case studies, (3) critical case studies, and (4) studies of hard- to-find populations.
1. Pilot studies. These are studies done before running a larger study. In 1999, Katherine Browne, Carla Freeman, and Zobeida Bonilla began a comparative ethnographic study of women entrepreneurs in Martinique, Barbados, and Puerto Rico—that is, in the French-, English-, and Spanish-speaking Caribbean. In a large, multisite study like this, it pays to spend time on pilot research. Each member of the team did 30 in-depth interviews with women who were engaged in a wide range of enterprises, who were of different ages, and who came from one- and two-parent homes. This helped the team develop their research instruments and provided the baseline for the larger project (Browne 2001).
And speaking of instruments, when you do surveys to test hypotheses, make sure that you test all your scales with a pilot sample. More about all this in chapter 11, on scales.
2. In intensive case studies, the object is often to identify and describe a cultural phenomenon. Dickerson et al. (2000) studied the experiences of American Indian graduate nursing students and cultural barriers that might lead the students to drop out of their training. Dickerson et al. found and interviewed 11 students who were enrolled in an advanced nurse practitioner program. Samples don’t get much more purposive than this, and they don’t get much more appropriate, either.
Life history research and qualitative research on special populations (drug addicts, trial lawyers, shamans) rely on judgment sampling. Barroso (1997), for example, studied a purposive sample of 14 men and six women in the Tampa, Florida, area, all of whom had lived with AIDS for at least 3 years.
Finally, researchers don’t usually pull research sites—villages, tribal encampments, hospitals, school systems—out of a hat. They rely on their judgment to find one that reflects the things they are interested in.
3. Critical case studies. These are done in all fields of science and have long been the basis, by deduction, for the development of theory. Freud based his theory of psychosexual development on a few critical cases from his practice. Steward based his theory of multilineal evolution on a few critical cases from archeology. Political scientists study cases like the Orange Revolution in Ukraine for clues about the transition from autocracy to democracy (McFaul 2007).
Choosing key informants in ethnographic research is a form of critical-case sampling. It would be pointless to select a handful of people randomly from a population and try to turn them into trusted key informants.
4. We almost always have to rely on purposive sampling in the study of hard-to-find populations.
Think about locating and interviewing refugees from Somalia and Ethiopia living in a large American city. Many of these people experienced torture and don’t exactly welcome researchers who want to ask them a lot of questions. This was the problem facing researchers in Minneapolis (see Jaranson et al. 2004; Spring et al. 2003). The study design called for a quota sample of 1,200 respondents, including 300 Oromo women, 300 Oromo men, 300 Somali women, and 300 Somali men. The study team recruited male and female interviewers from the community—people who shared ethnicity, language, and religion with the people they were trying to locate and interview. The project team sent out fliers, placed announcements in church bulletins, and made presentations at meetings of Oromo and Somali organizations. The interviewers also used their own social networks to locate potential respondents. Over 25 months, the team built trust in the community and wound with 1,134 of the 1,200 interviews called for in the study.
Kimberly Mahaffy (1996) was interested in how lesbian Christians deal with the cogni?tive dissonance that comes from being rejected by mainstream Christian churches. Mahaffy sent letters to gay Christian organizations, asking them to put an ad for potential respondents in their newsletters. She sent flyers to women’s bookstores and to lesbian support groups, asking for potential respondents to get in touch with her.
Eventually, Mahaffy got 163 completed questionnaires from women who fit the criteria she had established for her research, including 44 from women who self-identified as born-again or evangelical Christians. Mahaffy could not possibly have gotten an unbiased sample of lesbian Christians, but the corpus of data that she collected from her respondents had all the information she needed to answer her research questions (Further Reading: purposive sampling).