CHAPTER 2
POPULATIONS AND SAMPLES
This chapter is an introductory chapter on sampling. In Section 2.1 we present
the basic concepts of samples and populations. In Section 2.2 we discuss the most
commonly used methods of taking samples and the reasons for using a random sample.
Methods of selecting a random sample are given in Section 2.3. The characteristics
of a good sampling plan and the methods commonly used in the various types of
biomedical studies are described in Section 2.4.
2.1 BASIC CONCEPTS
Before presenting methods of taking samples, we define three basic concepts: sam-
ples, population, and target population. A brief discussion of the reasons for sampling
is also given.
In most research work, a set of data is not primarily interesting for its own sake,
but rather for the way in which it may represent some other, larger set of data. For
example, a poll is taken in which 100 adults are asked whether they favor a certain
measure. These 100 adults live in a small communitity that has 2500 adults living
in it. The opinions of the 100 people may be of very minor importance except as an
indication of the opinions prevailing among the 2500 adults. In statistical terminology,
Basic Statistics: A Primer for the Biomedical Sciences, Fourth Edition.
By Olive Jean Dunn and Virginia A. Clark
Copyright @ 2009 John Wiley & Sons, Inc.
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