chapter4small - Section 4.1 Should We Experiment or Should...

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Section 4.1 Should We Experiment or Should We Merely Observe? May 11, 2009 1 4 Gathering Data 4.1 Should We Experiment or Should We Merely Observe? Example: Does cell-phone use cause brain cancer? (a) Conduct an observational study (i.e., take a survey) among humans. * Survey people with and without brain cancer, to determine their rates of cell-phone usage. * Survey people with and without brain cancer, to determine their rates of cell-phone usage. What are the drawbacks to this observational study? * Hence, the association does not necessarily imply a causation. * Hence, the association does not necessarily imply a causation. (b) Conduct an experiment with humans. * Then compare the rates of brain cancer for the two groups. * Then compare the rates of brain cancer for the two groups. What are the drawbacks to this experiment? * The experiment takes too long. It would be diFcult to monitor cell-phone usage. * The experiment takes too long. It would be diFcult to monitor cell-phone usage. (c) Conduct an experiment with mice. * Then compare the rates of brain cancer for the two groups. * Then compare the rates of brain cancer for the two groups. What are the drawbacks to this experiment? * The e±ects of radiation on mice may be di±erent than on humans. * The e±ects of radiation on mice may be di±erent than on humans.
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Section 4.2 What are Good Ways and Poor Ways to Sample? May 11, 2009 2 A Survey and a Census Example: Suppose we are interested in the population proportion of American adults who support the President’s foreign policy in Afghanistan? Ideally, take a . What would be the disadvantages ? * A census requires much time and money. * A census requires much time and money. What would be the advantages ? * With everyone polled (unlike a sample), not as much error is introduced. * With everyone polled (unlike a sample), not as much error is introduced. Instead, take a . Defnition: “A sample survey selects a sample of people from a population and interviews them to collect data.” What would be the advantages ? * A survey can be performed relatively quickly and cheaply. * A survey can be performed relatively quickly and cheaply. What would be the disadvantages ? * With fewer people polled (than a census), additional error is introduced. * With fewer people polled (than a census), additional error is introduced. 4.2 What are Good Ways and Poor Ways to Sample? Defnition: “A simple random sample of n subjects from a population is one in which each possible sample of that size has the same chance of being selected.”
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Section 4.2 What are Good Ways and Poor Ways to Sample? May 11, 2009 3 Data collection may consist of personal interview , telephone interview (perhaps via random digit dialing), or self-administered questionnaire .
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chapter4small - Section 4.1 Should We Experiment or Should...

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