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Sampling

Sampling. Learning Objectives. To become familiar with sample design terminology. To learn about practical and “sufficiency of information” reasons for selecting a sample. To understand the differences between “probability” and “nonprobability” sampling methods.

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Sampling

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  1. Sampling

  2. Learning Objectives • To become familiar with sample design terminology. • To learn about practical and “sufficiency of information” reasons for selecting a sample. • To understand the differences between “probability” and “nonprobability” sampling methods. • To acquire the skills to administer different types of samples. • To be able to develop a sample plan.

  3. Sample • Units (typically people) selected from the population of interest for purposes being able to draw conclusions about that population of interest. • We use the “sample” statistics as a representation of the true “population” parameters (value).

  4. Census Vs. Sample • Sampling less expensive • Sampling less time • Sampling may be more accurate • Sampling vs nonsampling error • Fresh respondents

  5. When Would One Conduct a Census • Feasible (due to size of pop.) • Necessary (due to differences in the population)

  6. Sampling Process • Identify the population of interest • Determine the sampling frame • Select the sampling procedure • Determine the sample size • Execute sampling • Collect data from respondents • Assess nonresponse error

  7. So, what is the population of interest?

  8. Define the Population of Interest

  9. Sampling Frame • Listing of the population units from which the sample is drawn.

  10. Sampling Unit Pertains to the basic unit of investigation, e.g. person and e-mail address, person and address.

  11. Universe, Population, Frame, Sample Universe: U.S. Residents, 18+ Population: Males, 18+ Sample Malhotra, N. K. (1999). Marketing research: An applied orientation. (International 3rd edition). London: Prentice Hall.

  12. Coverage of a Target Population by a Sampling Frame Population of Interest Target Population

  13. Coverage of a Target Population by a Sampling Frame List of names & addresses, phone numbers, or e-mail addresses Sampling Frame Population

  14. Coverage of a Target Population by a Sampling Frame Sampling Frame Population Covered Population Target Population

  15. Selecting the Sampling Procedure • Probability Sample: EVERY sample member has a known, equal, non-zero chance for inclusion in the sample. • Nonprobability Sample: Introduces some form of convenience into the process that makes knowledge of the above not possible.

  16. Probability • Simple Random • Stratified • Cluster

  17. Nonprobability • Convenience • Judgment • Quota • Snowball

  18. As a reminder, Sampling Process • Identify the population of interest • Determine the sampling frame • Select the sampling procedure • Determine the sample size • Execute sampling • Collect data from respondents • Assess nonresponse error

  19. Determining the Sample Size • The size of a sample has nothing to do with its representativeness. • Representativeness is dependent on the sample plan. Sample size affects the sample accuracy! • Sample accuracy refers to how close the sample’s statistic is to the true population value (parameter) it represents.

  20. Criteria to Consider in Determining Sample Size • Precision Level • Confidence Level • Population Variability

  21. Sample Size Determination zq2s2 n = Where: H2 n = sample size zq2 = z value for confidence level s2 = est. of pop. standard deviation H2 = precision level

  22. Typical Sample Sizes - People Regional or Special Number of Subgroups National

  23. Regional or Special Number of Subgroups National Typical Sample Sizes - Institutions

  24. Additional Factors to Consider • Response Rate • Deliverable Rate • Completion Rate

  25. How About an In-Class Exercise?Working Individually… • Identify the Population of Interest for your study? • Identify the Sampling Frame? • Identify the Sampling Unit? • How will you select the Sampling Units?

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