Chapter 4: Q 1.1. (page 211)
A farmer brings a juice company several crates of oranges each week. A company inspector looks at oranges from the top of each crate before deciding whether to buy all the oranges.
Convenience sampling.
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Headache relief Doctors identify “chronic tension- type headaches” as headaches that occur almost daily for at least six months. Can antidepressant medications or stress management training reduce the number and severity of these headaches? Are both together more effective than either alone? Investigators compared four treatments: antidepressant alone, placebo alone, antidepressant plus stress management, and placebo plus stress management. The headache sufferers named in the following table have agreed to participate in the study.
(a) Outline the design of the experiment. What is this type of design called?
(b) Explain how you would randomly assign the subjects to the four treatment groups. Then carry out your random assignment.
Each of the following is a source of error in a sample survey. Label each as sampling error or non sampling error, and explain your answers.
(a) The telephone directory is used as a sampling frame.
(b) The person cannot be contacted in five calls.
(c) Interviewers choose people walking by on the sidewalk to interview.
2. A survey paid for by makers of disposable diapers found that of the sample opposed banning disposable diapers. Here is the actual question:
Customer satisfaction A department store mails a customer satisfaction survey to people who make credit card purchases at the store. This month,
people made credit card purchases. Surveys are mailed to of these people, chosen at random, and people return the survey form. Identify the
population and the sample.
Acupuncture and pregnancy A study sought to determine whether the ancient Chinese art of acupuncture could help infertile women become pregnant.41 One hundred sixty healthy women undergoing treatment with artificial insemination were recruited for the study. Half of the subjects were randomly assigned to receive acupuncture treatment minutes before embryo transfer and again
minutes after the transfer. The remaining subjects were instructed to lie still for minutes after the embryo transfer.
Results: In the acupuncture group, women became pregnant. In the control group, women became pregnant.
(a) Describe how the three principles of experimental design were addressed in this study.
(b) The difference in the percent of women who became pregnant in the two groups is statistically significant. Explain what this means to someone who
knows little statistics.
(c) Explain why the placebo effect prevents us from concluding that acupuncture caused the difference in pregnancy rates.
The effects of day care Does day care help low- income children stay in school and hold good jobs later in life? The Carolina Abecedarian Project (the name suggests the ABCs) has followed a group of children since . Back then, these individuals were all healthy but low-income black infants in Chapel Hill, North Carolina. All the infants received nutritional supplements and help from social workers. Half were also assigned at random to an intensive preschool program.
(a) Explain the purpose of each of the three experimental design principles.
(b) Describe how each of these principles was used in this study.
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