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Chapter 1: Introduction and Graphical Displays
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The illustration for a random sample of size
is depicted in
Figure 1-5.
Figure 1- 5:
Illustration for a random sample of size
n
Definition: Simple Random Sample of Size
n
A simple random sample of size
is one in which every group of size
has
an equal chance of being selected.
For instance, in a lottery game in which five numbers are selected, this will
be a simple random sample of size five, since each group of size five will
have an equal chance of being selected.
In certain circumstances, random samples may not be adequate in the sense
that it may not provide sufficient information about subgroups within the
population. For instance, you may be interested in knowing the proportion
of one particular ethnic group who are Methodists. A random sample of
100, say, may yield only 10 persons in that particular ethnic group. This
number of 10 may be too small to be useful for any reliable statistical
inferences. Thus, the researcher may need to obtain samples using other
procedures. Other sampling methods include
stratified
sampling,
cluster
sampling,
systematic
sampling, and
convenience
sampling.
Stratified Sample
Sometimes researchers may be interested in investigating characteristics of
certain subgroups of the population, such as political affiliation, church