sm_chapter_04

# sm_chapter_04 - CHAPTER 4 SOLUTIONS AND MINI-PROJECT NOTES...

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CHAPTER 4 SOLUTIONS AND MINI-PROJECT NOTES CHAPTER 4 HOW TO GET A GOOD SAMPLE EXERCISE SOLUTIONS 4.1 a. Cluster sampling; unlikely to be biased if all passengers complied. b. Systematic sampling; likely to be biased for a number of reasons. For instance, ground-floor residents may be more susceptible to crime and thus have more extreme views. Those at home during the day may differ from those not at home, and leaving a notice for the others to call would introduce bias because only those with strong opinions would be likely to do so. c. Stratified sample; not likely to be biased. d. Convenience or haphazard sample; likely to be biased for a number of reasons. The most obvious is that the people who looked approachable and had time to answer questions would be the ones chosen. 4.2 A proportion is a part of a whole and a percentage is that same part multiplied by 100. For instance, 1/10th of something is a proportion, equal to .10, and is also 10%. 4.3 The example should be one for which there is a systematic difference that would line up with the way the sample is collected. 4.4 a . 200 / 1 = .07 or 7%. b. 80% ± 7% = 73% to 87%. c. You would get a different result tomorrow if you sampled a different collection of 200 people. But presumably he is not referring to sampling variability, and what he means is that in two years time the true proportion of parents in the population who felt uninformed would have changed as well. 4.5 a. A unit is a freshman at a two- or four-year college or university in the United States in Fall 1997, the population is all such students, the sample is the set of 252,082 students who were surveyed. b. A stratified random sample, in which schools were the strata. c. A cluster sample, where each school is a cluster. d. It would be difficult to obtain a list of all first-year students from which to select a simple random sample. It would be easier to obtain a list of schools, and then either contact each school and ask them to provide a random sample (as in part b) or first select a random sample of schools and then obtain a list of all first-year students at those schools (as in part c). 4.6 These results are more likely to reflect what is capturing students’ attention each year, rather than increased apathy. For instance, in years in which the economy is bad and jobs are scarce, students tend to be more concerned with finding jobs. In years in which there are political issues affecting students, they are likely to be more concerned with politics. 4.7 a. The population of units is all customers of that airline; the measurements are their opinions about the airline. Units in the sample are the passengers on the selected 25 flights, and the sample measurements are their opinions. b. The population of units is all residents of the city, and the measurements are their opinions on gun control. The sample of units consists of those who were either at home and answered or phoned later and answered, and the measurements are their expressed opinions on gun control.

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