Ofelementscalledclusters

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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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