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Designing Samples


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Designing Samples

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