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Chapter 4: Q 40. (page 230)
When we take a census, we attempt to collect data from
(a) a stratified random sample.
(b) every individual selected in an SRS.
(c) every individual in the population.
(d) a voluntary response sample.
(e) a convenience sample.
The correct option is (c) every individual in the population.
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Getting teachers to come to school Elementary schools in rural India are usually small, with a single teacher. The teachers often fail to show up for work. Here is an idea for improving attendance: give the teacher a digital camera with a tamperproof time and date stamp and ask a student to take a photo of the teacher and class at the beginning and end of the day. Offer the teacher better pay for good attendance, verified by the photos. Will this work? Researchers obtained permission to use 120 rural schools in Rajasthan for an experiment to find out.
(a) Explain why it would not be a good idea to offer better pay for good attendance to the teachers in allschools and then to compare this year’s attendance with last year’s.
(b) Write a few sentences describing how you would design this experiment.
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.
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.
In the cornfield An agriculture researcher wants to compare the yield of five corn varieties: A, B, C, D, and E. The field in which the experiment will be carried out increases in fertility from north to south. The researcher therefore divides the field into twenty five plots of equal size, arranged in five east–west rows of five plots each, as shown in the diagram.
(a) Explain why a randomized block design would be better than a completely randomized design in this setting.
(b) Should the researcher use the rows or the columns of the field as blocks? Justify your answer.
(c) Use technology or Table D to carry out the random assignment required by your design. Explain your method clearly.
Got deodorant? A group of students wants to perform an experiment to determine whether Brand A or Brand B deodorant lasts longer. One group member
suggests the following design: Recruit student volunteers—male and female. Separate by gender, since male and female bodies might respond
differently to deodorant. Give all the males Brand A deodorant and all the females Brand B. Have each student rate how well the deodorant is still working at the end of the school day on a 0 to 10 scale. Then compare ratings for the two treatments.
(a) Identify any flaws you see in the proposed design for this experiment.
(b) Describe how you would design the experiment. Explain how your design addresses each of the problems you identified in (a).
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