SUBJECTS AND SAMPLING
Purposive sampling is not widely used in quantitative studies. In qualitative research, on the other hand, some type of purposive sam- pling is almost always used. Purposive sampling is illustrated by the fol- lowing excerpts. Further discussion of sampling for qualitative studies is included in Chapter 10.
Introductory psychology students
: kxahip/&3: Purposive sainpring (N
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volunteered to take the Dog-
matism Scale (Form
for experimental credit. From the upper and lower
quartiles on the Dogmatism Scale, 44 high and 44 low dogmatic subjects
selected for the experiment.”
636-637) Notice also that this is a convenience sample.
: ’ were ‘.
“Four second-grade and two firstgrade teachers from public the San Francisco Bay Area participated in the study. All were
at least 10 years of teaching experience at the
recruited to include as wide a range of backgrounds and in the teaching of mathematics as possible. Some were
mended by their principals as being strong mathematics teachers who had been involved in various and curriculum development ties. Others agreed to participate in the study because they were inter-
,I ; ers were
proaches :. -
but did not consider themselves to be particularly outstanding mathematics teachers.” (Putnam, 1987, pp. 17-18)
“Six schools were selected from the 26 in the district. Selection was by the need to capture the variability of retention practices within the district. For example, two schools with high-retaining and three with low-retaining kindergartens were selected, along with one school that had developmental kindergarten and a transition (between kindergarten and
1 1 )I
first grade) class.” (Smith and
1988, p. 311)
Quota Sampling Quota sampling is used when the researcher is unable to take a probability sample but still wants a sample that is representative of the entire population. Different composite profiles of major groups in the population are identified, and then subjects are selected,
to represent each
A type of quota sampling that is com-
mon in educational research is conducted to represent geographic areas or types of communities, such as urban, rural, and suburban.
a state is divided into distinct geographic areas, and cases are se-
lected to represent each area. As in availability and purposive sampling, there is a reliance on the decisions of the researcher the sample, and appropriate caution should be used in interpreting the