the logic of sampling. key sampling concepts sampling (two types) element population sample sampling...
TRANSCRIPT
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The Logic of Sampling
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Key Sampling Concepts
• Sampling (two types)• Element• Population• Sample• Sampling Frame• Representative Sample
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Application of Sampling Terms
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Types of Samples
• Probability -- Strictly following two rules.• Non Probability -- Failing to follow the two
rules
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Types of Probability Samples
• Simple Random Sample (SRS)• Systematic Random Sample• Stratified Random Sample• Cluster Sample
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Simple Random Sample
• Every element has an equal chance of selection
• No element can be selected more than once
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Example of a good random sample outcome
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Simple Random Sample
• Every element has an equal chance of selection
• No element can be selected more than once
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Systematic Random SampleSampling Frame
Nth ElementA simple random sample employing a sample
frame.
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Stratified Random Sample
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Cluster Sample
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Non probability samples
• Convenience (available to researcher)• Snowball (available connections)• Quota (stratified without randomness) • Informant (case study/social history)• Focus Groups
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What’s the difference?How important is the difference?
Probability samples can be generalized to a population; while non-probability samples cannot.
Non-probability offer an in depth understanding and are most often: “I don’t know what I am seeking until after I find it.”
Following is an illustration:
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Overview of Sample ProblemsHite, S. (1987). Women in Love: A Cultural Revolution in Progress. NY: Alfred A. Knopf.
Laumann, E. O., Gagnon, J. H., Michael, R. T. & Michaels, S. (1994). The Social Organization of Sexuality: Sexual Practices in the United States. Chicago: University of Chicago Press.
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Sample Size Selection
The problem with the following formula:It is calibrated for dichotomous data. The sample size will increase with the number of options given to the subject.
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Do NOT Forget!!!!
Regardless of what formula one uses,
always increase the sample size by 20%.
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Excel
• RANDBETWEEN – Returns a random number between the numbers you specify.
• RAND – Returns a random number greater than or equal to 0 and less than 1, evenly distributed (changes on recalculation).