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.
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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Get started for freeThe 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.
Cocoa and blood flowA study conducted by Norman Hollenberg, professor of medicine at Brigham and Women’s Hospital and Harvard Medical School,
involved healthy people aged . Each subject consumed a cocoa beverage containing milligrams of flavonols (a class of flavonoids) daily
for five days. Using a finger cuff, blood flow was measured on the first and fifth days of the study. After five days, researchers measured what they called “signifi-
cant improvement” in blood flow and the function of the cells that line the blood vessels. What flaw in the design of this experiment makes it impossible to say
whether the cocoa really caused the improved blood flow? Explain.
In an interesting experiment, researchers examined the effect of ultrasound on birth weight. Pregnant women participating in the study were randomly assigned to one of two groups. The first group of women received an ultrasound; the second group did not. When the subjects’ babies were born, their birth weights were recorded. The women who received the ultrasounds had heavier babies.
Did the experimental design take the placebo effect into account? Why is this important?
Apartment living You are planning a report on apartment living in a college town. You decide to select three apartment complexes at random for
in-depth interviews with residents.
(a) Explain how you would use a line of Table D to choose an SRS of 3 complexes from the list below. Explain your method clearly enough for a classmate to obtain your results.
(b) Use line 117 to select the sample. Show how you use each of the digits.
A simple random sample of adult Americans is selected, and each person is asked the following question: “In light of the huge national deficit, should the government at this time spend additional money to establish a national system of health insurance?” Only of those responding answered “Yes.” 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.
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