Chapter 1: Problem 4
What is random sampling? Why is it used and how does it compare with convenience sampling?
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These are the key concepts you need to understand to accurately answer the question.
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Chapter 1: Problem 4
What is random sampling? Why is it used and how does it compare with convenience sampling?
These are the key concepts you need to understand to accurately answer the question.
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The survey has bias. (a) Determine the type of bias. (b) Suggest a remedy. To determine the public's opinion of the police department, the police chief obtains a cluster sample of 15 census tracts within his jurisdiction and samples all households in the randomly selected tracts. Uniformed police officers go door to door to conduct the survey.
Define simple random sampling.
Determine whether the study depicts an observational study or an experiment. Two hundred people are asked to perform a taste test in which they drink from two randomly placed, unmarked cups and asked which drink they prefer.
You wonder whether green tea lowers cholesterol. (a) To research the claim that green tea lowers LDL (so-called bad) cholesterol, you ask a random sample of individuals to divulge whether they are regular green tea users or not. You also obtain their LDL cholesterol levels. Finally, you compare the LDL cholesterol levels of the green tea drinkers to those of the non-green tea drinkers. Explain why this is an observational study. (b) Name some lurking variables that might exist in the study (c) Suppose, instead of surveying individuals regarding their tea-drinking habits, you decide to conduct a designed experiment. You identify 120 volunteers to participate in the study and decided on three levels of the treatment: a placebo, one cup of green tea daily, two cups of green tea daily. The experiment is to run for one year. The response variable will be the change in LDL cholesterol for each subject from the beginning of the study to the end. What type of experimental design is this? (d) Explain how you would use blinding in this experiment. (e) What is the factor? Is it qualitative or quantitative? (f) What factors might you attempt to control in this experiment. (g) Explain how to use randomization in this experiment. How does randomization neutralize those variables that are not controlled? (h) Suppose you assigned 40 subjects to each of the three treatment groups. In addition, you decided to control the variable exercise by having each subject perform 150 minutes of cardiovascular exercise each week by walking on a treadmill. However, the 40 subjects in the placebo group decided they did not want to walk on the treadmill and skipped the weekly exercise. Explain how exercise is now a confounding variable.
A research objective is presented. For each, identify the population and sample in the study. A quality-control manager randomly selects 50 bottles of Coca-Cola that were filled on October 15 to assess the calibration of the filling machine.
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