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Sample Definitions Sample Types Rules for Simple Random Sample and Sample Size Selection

Sample Definitions Sample Types Rules for Simple Random Sample and Sample Size Selection. Basic Terms. Sampling Element Population Sample Sampling Frame Representative Sample v. Bias Sample Rules for getting a good representative sample

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Sample Definitions Sample Types Rules for Simple Random Sample and Sample Size Selection

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  1. Sample DefinitionsSample TypesRules for Simple Random Sampleand Sample Size Selection

  2. Basic Terms • Sampling • Element • Population • Sample • Sampling Frame • Representative Sample v. Bias Sample Rules for getting a good representative sample • Every element has an equal chance of being selected. • No element can be selected more than once.

  3. Types of Sampling • Probability • Non-probability

  4. Probability Sampling • Simple Random Sample (SRS) • Systematic Random Sample • Stratified Random Sample • (Proportional Stratified Random Sample) • Cluster (Random) Sample

  5. Non-Probability Sampling • Availability Sample • Purposeful/Judgmental • Snowball • Quota • Informant • Focus Group • Criteria

  6. Rules for a Collecting a Simple Random Sample (SRS) • Every subject within a population must have an equal chance of being selected. • No subject within a population may be selected more than once. Note: Violation of either one of these rules can produce false generalizations. In addition, compliance with these rules is very expensive. For example, the standard fee to conduct a national phone survey is $1,500 per minute. Because of this expense, social service agencies rarely collect adequate samples. Therefore their results cannot be trusted.

  7. Sample Size Selection • The problem with the following formula: • It is celebrated for dichotomous data. The sample size will increase with the number of options given to the subject.

  8. One More Rule There are many formulas for determining a sample size. Regardless of what formula you use, the rule of thumb is, “increase your sample size by 20%.”

  9. Check out the following • http://stattrek.com/Lesson3/SamplingTheory.aspx?Tutorial=Stat’ • http://www.youtube.com/watch?v=Qo2K46Hr3lc • http://www.youtube.com/watch?v=g9H_XGqmvEs

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