Chapter 1: Problem 4
What is random sampling? Why is it used and how does it compare with convenience sampling?
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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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Researchers wanted to determine whether the stomach shrinks as a result of dieting. To do this, they randomly divided 23 obese patients into two groups. The 14 individuals in the experimental group were placed on a diet that allowed them to consume 2508 kilojoules \((\mathrm{kJ})\) per day for 4 weeks. The 9 subjects in the control group ate as they normally would. To assess the size of the stomach, a latex gastric balloon was inserted into each subject's stomach and filled with the maximum amount of water that could be tolerated by the patient. The volume of water was compared to the volume that could be tolerated at the beginning of the study. The experimental subjects experienced a \(27 \%\) reduction in gastric capacity, while the subjects in the control group experienced no change in gastric capacity. It was concluded that a reduction in gastric capacity occurs after a restricted diet. (a) What type of experimental design is this? (b) What is the population that the results of this experiment apply to? (c) What is the response variable in this study? Is it qualitative or quantitative? (d) What are the treatments? (e) Identify the experimental units. (f) Draw a diagram similar to Figure \(7,8,\) or 10 to illustrate the design.
A research objective is presented. For each, identify the population and sample in the study. Folate and Hypertension Researchers want to determine whether or not higher folate intake is associated with a lower risk of hypertension (high blood pressure) in women ( 27 to 44 years of age). To make this determination, they look at 7373 cases of hypertension in these women and find that those who consume at least 1000 micrograms per day \((\mu \mathrm{g} / \mathrm{d})\) of total folate had a decreased risk of hypertension compared with those who consume less than \(200 \mu \mathrm{g} / \mathrm{d}\).
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.
Discuss a possible advantage of offering rewards or incentives to increase response rates. Are there any disadvantages?
What is the role of randomization in a designed experiment? If you were conducting a completely randomized design with three treatments and 90 experimental units, describe how you would randomly assign the experimental units to the treatments.
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