Chapter 4: Q 2.3. (page 240)
What is the purpose of the control group in this experiment?
Short Answer
A control group allows the difference in test group outcomes to be compared.
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Chapter 4: Q 2.3. (page 240)
What is the purpose of the control group in this experiment?
A control group allows the difference in test group outcomes to be compared.
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Eat well and exercise Most American adolescents don鈥檛 eat well and don鈥檛 exercise enough. Can middle schools increase physical activity among their students? Can they persuade students to eat
better? Investigators designed a 鈥減hysical activity intervention鈥 to increase activity in physical education classes and during leisure periods throughout the school day. They also designed a 鈥渘utrition intervention鈥 that improved school lunches and offered ideas for healthy home-packed lunches. Each participating school was randomly assigned to one of the interventions, both interventions, or no intervention. The investigators observed physical activity and lunchtime
consumption of fat.
What kind of error? Which of the following are sources of sampling error and which are sources of non-sampling error? Explain your answers.
(a) The subject lies about past drug use.
(b) A typing error is made in recording the data.
(c) Data are gathered by asking people to mail in a coupon printed in a newspaper.
Dead trees On the west side of Rocky Mountain National Park, many mature pine trees are dying due to infestation by pine beetles. Scientists would like to
use sampling to estimate the proportion of all pine trees in the area that have been infected.
(a) Explain why it wouldn鈥檛 be practical for scientists to obtain an SRS in this setting.
(b) A possible alternative would be to use every pine tree along the park鈥檚 main road as a sample. Why is this sampling method biased?
(c) Suppose that a more complicated random sampling plan is carried out, and that of the pine trees in the sample are infested by the pine beetle. Can
scientists conclude that 35% of all the pine trees on the west side of the park are infested? Why or why not?
A simple random sample of adult Americans is selected, and each person is asked the following question: 鈥淚n light of the huge national deficit, should the government at this time spend additional money to establish a national system of health insurance?鈥 Only of those responding answered 鈥淵es.鈥 This survey
(a) is reasonably accurate since it used a large simple random sample.
(b) needs to be larger since only about people were drawn from each state.
(c) probably understates the percent of people who favor a system of national health insurance.
(d) is very inaccurate but neither understates nor overstates the percent of people who favor a system of national health insurance. Since simple random sampling was used, it is unbiased.
(e) probably overstates the percent of people who favor a system of national health insurance.
Effects of binge drinking A common definition of 鈥渂inge drinking鈥 is or more drinks at one sitting for men and or more for women. An observational study
finds that students who binge drink have lower average GPA than those who don鈥檛. Identify a lurking variable that may be confounded with the effects of binge drinking. Explain how confounding might occur.
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