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Chapter 4: Q T4.2. (page 274)
You want to take a simple random sample (SRS) of of the students who live in a dormitory on campus. You label the students 001 to 816 in alphabetical order. In the table of random digits, you read the entries.
The first three students in your sample have labels
The correct option is (e)
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Two essential features of all statistically designed experiments are
(a) comparing several treatments; use the double-blind method.
(b) compare several treatments; use the chance to assign subjects to treatments.
(c) always have a placebo group; use the double-blind method.
(d) use a block design; use the chance to assign subjects to treatments.
(e) use enough subjects; always have a control group.
The ABC program Nightline once asked whether the United Nations should continue to have its headquarters in the United States. Viewers were invited to call one telephone number to respond 鈥淵es鈥� and another for 鈥淣o.鈥� There was a charge for calling either number. More than callers responded, and said 鈥淣o.鈥�
Sampling gravestones The local genealogical society in Coles County, Illinois, has compiled records on all gravestones in cemeteries in the county from the years to Historians plan to use these records to learn about African Americans in Coles County鈥檚 history. They first choose an SRS of records to check their accuracy by visiting the actual gravestones.
(a) Explain how you would use technology or Table D to choose the SRS. Your description should be clear enough for a classmate to obtain your results.
(b) Use your method from (a) to choose the first gravestones.
Cocoa and blood flowA study conducted by Norman Hollenberg, professor of medicine at Brigham and Women鈥檚 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 鈥渟ignifi-
cant improvement鈥� 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.
More rain for California? The changing climate will probably bring more rain to California, but we don鈥檛 know whether the additional rain will come during the
winter wet season or extend into the long dry season in spring and summer. Kenwyn Suttle of the University of California at Berkeley and his coworkers carried
out an experiment to study the effects of more rain in either season. They randomly assigned plots of open grassland to three treatments: added water equal to of annual rainfall either during January to March (winter) or during April to June (spring), and no added water (control). Thirty-six circular plots of area square meters were available (see the photo), of which were used for this study. One response variable was total plant biomass, in grams per square meter, produced in a plot over a year.
(a) Outline the design of the experiment. What is this type of design called?
(b) Explain how you would randomly assign the experimental units to the three treatments. Then carry out your random assignment.
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