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Unformatted text preview: each stratum. Formulas are available for combining the stratum
Formulas are available for combining the stratum sample results into one population parameter
sample results into one population parameter estimate.
estimate. Advantage: If strata are homogeneous, this method
Advantage: If strata are homogeneous, this method is as “precise” as simple random sampling but with
is as “precise” as simple random sampling but with a smaller total sample size.
a smaller total sample size. Example: The basis for forming the strata might be
Example: The basis for forming the strata might be department, location, age, industry type, and so on.
department, location, age, industry type, and so on.
ECO 3411 52 Cluster Sampling The population is first divided into separate groups
The population is first divided into separate groups of elements called clusters.
of elements called clusters. Ideally, each cluster is a representative smallscale
Ideally, each cluster is a representative smallscale version of the population (i.e. heterogeneous group).
version of the population (i.e. heterogeneous group). A simple random sample of the clusters is then taken.
A simple random sample of the clusters is then taken. All elements within each sampled (chosen) cluster
All elements within each sampled (chosen) cluster form the sample.
form the sample. ECO 3411 53 Cluster Sampling Example: A primary application is area sampling,
Example: A primary application is area sampling, where clusters are city blocks or other welldefined
where clusters are city blocks or other welldefined areas.
areas. Advantage: The close proximity of elements can be
Advantage: The close proximity of elements can be cost effective (i.e. many sample observations can be
cost effective (i.e. many sample observations can be obtained in a short time).
obtained in a short time). Disadvantage: This method generally requires a
Disadvantage: This method generally requires a larger total sample size than simple or stratified
larger total sample size than simple or stratified random sampling.
random sampling. ECO 3411 54 Convenience Sampling
• It is a nonprobability sampling technique. Items are
included in the sample without known probabilities of
being selected.
• The sample is identified primarily by convenience.
• Advantage: Sample selection and data collection are
relatively easy.
• Disadvantage: It is impossible to determine how
representative of the population the sample is.
• Example: A professor conducting research might use
student volunteers to constitute a sample. ECO 3411 55 Judgment Sampling
• The person most knowledgeable on the subject of the
study selects elements of the population that he or she
feels are most representative of the population.
• It is a nonprobability sampling technique.
• Advantage: It is a relatively easy way of selecting a
sample.
• Disadvantage: The quality of the sample results depends
on the judgment of the person selecting the sample.
• Example: A reporter might sample three or four senators,
judging them as reflecting the general opinion of the
senate.
ECO 3411 56 END LESSON 1 ECO 3411 57...
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 Winter '08
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