UK STA 200 - Chapter 2 Samples, Good and Bad

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Chapter 2Thought Question 1Thought Question 2Thought Question 3Thought Question 5Bad Sampling PlansConvenience SamplingVoluntary ResponseSimple Random SamplingSlide 10Key ConceptsChapter 2 1Chapter 2Samples, Good and BadChapter 2 2Thought Question 1Popular magazines often contain surveys that ask their readers to answer questions about hot topics in the news. Do you think the responses the magazines receive are representative of public opinion? Explain why or why not.Chapter 2 3Thought Question 2The Cable News Network (CNN) often asks its viewers to call the network with their opinions on certain political issues, like whether or not they favor current foreign policy. Do you think the results of these polls represent the feelings of the general population? Do you think they represent the feelings of all those watching CNN at the time? Explain.Chapter 2 4Thought Question 3Researchers in health and nutrition often study the effectiveness of new supplements by providing subjects with both the new supplement and a “fake” supplement made to look like the real thing. Do you think the results would be biased if the person providing the products to the participants knew which was which?Chapter 2 5Thought Question 5Suppose you access an online listing of all courses at your institution, alphabetized by department, to determine what proportion of all courses have a statistics course as a prerequisite. If you decide to sample 50 courses in order to get a representative sample of courses, how would you select them? Would it be appropriate to simply select the first 50 courses listed?Chapter 2 6Bad Sampling PlansConvenience sampling–selecting individuals that are easiest to reachVoluntary response sampling–allowing individuals to choose to be in the sampleBoth of these techniques are biased–systematically favor certain outcomesChapter 2 7Convenience SamplingSampling mice from a large cage to study how a drug affects physical activity–lab assistant reaches into the cage to select the mice one at a time until 10 are chosenWhich mice will likely be chosen?–could this sample yield biased results?Chapter 2 8Voluntary ResponseTo prepare for her book Women and Love, Shere Hite sent questionnaires to 100,000 women asking about love, sex, and relationships.–4.5% responded–Hite used those responses to write her bookMoore (Statistics: Concepts and Controversies, 1997) noted:–respondents “were fed up with men and eager to fight them…”–“the anger became the theme of the book…”–“but angry women are more likely” to respondChapter 2 9Simple Random SamplingEach individual in the population has the same chance of being chosen for the sampleEach group of individuals (in the population) of the required size (n) has the same chance of being the sample actually selectedRandom selection:–“drawing names out of a hat”–random number table (see Table A in back of the text, or Random Number Table in back of the supplement)–computer softwareChapter 2 10Simple Random SamplingSuppose there are 800 courses at an institution, alphabetized by department (and numbered 001-800), and you decide to randomly select 50 of them to determine what proportion of all the courses have a statistics course as a prerequisite. Use a random number table to select which 50 courses to sample.Example: Courses with Statistics PrerequisiteTable A in back of the textbook:Pick a line and column at random: suppose we get line 111, column 3Random numbers: 605 130 929 700 412 712Random Number Table in back of the supplement:Pick a line and column at random: suppose we get line 6, column 2Random numbers: 092 507 965 673 211 040……Chapter 2 11Key ConceptsBiasConvenience SamplingVoluntary Response SamplingSimple Random


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UK STA 200 - Chapter 2 Samples, Good and Bad

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