Designing Samples
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Designing Samples

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Designing Samples Designing Samples Presentation Transcript

  • Surveys and Questioning
  • Class Survey
    • Some students and teachers are taking a survey today regarding advisory
    • In order to get reliable answers to the questions, we have to carefully design two things
      • The questions we ask and
      • The way we select people to take the survey.
    • An example of problems with questions is the Ann Landers Survey
  • Population and Sample
    • Entire group of individuals is called the population
      • Studying the whole population through contacting everyone is called a census
    • Selection of individuals to study from the population is a sample
      • We study a part in order to gain information about the whole because contacting everyone is too difficult
  • Types of Samples
    • Voluntary Response Sample
    • Convenience Sample
    • Simple Random Sample
    • Systematic Random Sample
    • Stratified Random Sample
    • Cluster Sample
  • Types of Samples
    • The types of samples that were used in the Ann Landers report and the Good Housekeeping report were Voluntary Response Samples
    • The type of sample that was used in the Kansas report was a Simple Random Sample
  • Voluntary Response Sample
    • People who choose themselves by responding to a general opinion
      • Biased: people with strong opinions are the ones that respond.
      • Call-in opinion polls: Example 5.2
      • Online polls: Example 5.3
  • Simple Random Sample
    • A simple random sample has two criteria
      • Every one must have an equal chance to be chosen
      • Each person must be chosen independently of all others
    • Draw names from a hat
    • Use a computer to randomly select people from your population list
    • Assign everyone a number and use a computer, calculator, or random digit table to select people at random
  • Sources of bias in sampling
    • Undercoverage: types of people left of a population list
    • Nonresponce: when an individual chosen for a sample cannot be contacted
    • Response Bias:
      • Behavior of the respondent (i.e. lying, failure to recall)
      • Behavior of the interviewer (i.e. gender of interviewer, order of answers, method of asking, wording of questions )
  • Sources of bias in sampling
    • As we saw in the different responses to Ann Landers and Good Housekeeping , the way the question is worded makes a difference.
    • Think about surveys that you see in your every day life.
      • What kind of samples are they using?
      • Are the questions leading or biased?
  • Example: Facebook Surveys
    • Here are some questions asked on a survey application ( yoursay ) on Facebook.
      • Is love overrated?
      • What is your political affiliation?
      • Should Fox News be allowed to call themselves news?
      • Should able bodied Americans get off of welfare and become productive members of society?
      • Since national health care will make such a huge change to America, should all voting Americans be allowed to vote on it?
      • Do you wish Ronald Regan could be President again?
      • Are you an idiot if you spend money to see Michael Moore’s movie “Capitalism” bashing capitalism?
  • Critical Thinking
    • Are the questions biased?
    • What kind of sample is being used?
    • Can we trust the results of these questions if they are biased or use biased sampling methods?
    • How could we revise the biased questions so they are not biased?