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

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Sample DefinitionsSample TypesRules for Simple
Random Sampleand Sample Size Selection
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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.

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Types of Sampling

• Probability
• Non-probability

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Probability Sampling

• Simple Random Sample (SRS)
• Systematic Random Sample
• Stratified Random Sample
• (Proportional Stratified Random Sample)
• Cluster (Random) Sample

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Non-Probability Sampling

• Availability Sample
• Purposeful/Judgmental
• Snowball
• Quota
• Informant
• Focus Group
• Criteria

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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.

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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.

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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.

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Check out the following

• http//stattrek.com/Lesson3/SamplingTheory.aspx?Tu
  torialStat
• http//www.youtube.com/watch?vQo2K46Hr3lc
• http//www.youtube.com/watch?vg9H_XGqmvEs