Complete all required problems and thier parts.
Overview
Chapter 7
Problems: 1, 5, 7, 8, 10, 14, 15, 16, 27, 36
Full Problems
7.1 The post-lunch dip is the drop in mental alertness after a midday meal. Does an extract of the leaves of the ginkgo tree reduce the post-lunch dip? A study assigns healthy people age 18 to 40 to take either ginkgo extract or a placebo pill. After lunch, they are asked to read seven pages of random letters and place an X over every e. We count the number of misses. What are the individuals, the treatments, and the response variable in this experiment?
7.5 The changing climate will probably bring more rain to California, but we don’t 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 a randomized controlled experiment to study the effects of more rain in either season. They randomly assigned plots of open grassland to 3 treatments: added water equal to 20% 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 70 square meters were available, of which 18 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 this experiment, following the model of Figure 7.3 (included below).
b. Number all 36 plots and choose 6 at random for each of the 3 treatments. Be sure to explain how you did the random selection.
FIGURE 7.3 Outline of a randomized comparative experiment to compare the effect of acupuncture, sham acupuncture, and placebo on headaches.
7.7 The timing of peanuts’ first introduction in children’s diet could affect allergic reactions, so physicians have debated whether to recommend early exposure or avoidance. A study enrolled 640 infants with severe eczema and split them into two groups based on whether they also had a diagnosed peanut allergy. Within each group, the researchers randomly assigned the infants to either completely avoid peanuts or consume peanuts in small amounts regularly until they reach 60 months of age. At the end of the study, an allergy test was conducted to establish which children had a peanut allergy.
a. What are the individuals, the treatments, and the response variable in this experiment?
b. What is the design of this experiment? Outline this design as in Figure 7.4 (included below).
c. Of the 640 infants in the study, only 98 had a diagnosed peanut allergy at the beginning of the study. Explain why you think the researchers decided to split the infants into two groups before randomly assigning them to the conditions.
FIGURE 7.4 Outline of a block design comparing two asthma care options for asthmatic children who are or are not exposed to smoke at home.
7.8 A bit of bedtime reading is a fairly common practice, and researchers examined whether changes in reading technology could impact sleep quality. They recruited a sample of 12 healthy adults to sleep in a sleep lab on two different days. In random order, participants read, for 30 minutes, a print book on one night and a light-emitting e-reader on the other night. Scalp electrodes were used to measure how long (in minutes) it took participants to reach a deep sleep stage. On average, the subjects took 12.3 minutes longer to reach deep sleep when they read with the e-reader than when they read with the book.
a. What are the individuals, the treatments, and the response variable in this experiment?
b. What is the design of this experiment?
c. Sleeping in an unfamiliar environment can create a sleep disturbance called the first night effect. Explain why it is important to select the print-book and e-reader nights in random order for each participant.
7.10 A 2015 peer-reviewed research article summarized its findings with both a bullet-point list of highlights and a graphical abstract. One bullet point reads, “Leptin stimulates lipolysis via sympathetic neurons in fat.” The graphic above it shows the silhouettes of a clearly overweight woman and a slim woman, with the words “leptin” and “lipolysis” connecting the brain to fat deposits in the lower back, and an arrow implying change from the overweight silhouette to the slim silhouette.
a. Go to http://dx.doi.org/10.1016/j.cell.2015.08.055 (Links to an external site.) and read the freely available abstract. Can you tell from this research summary who or what the individuals used in the research study were?
b. The extensive research described in the article was entirely performed on mice, a fact that is clearly mentioned in the methods and results sections of the full article. Discuss the validity of summarizing the research findings with a graphical abstract representing a woman.
c. While the research article is very thorough in many respects, the sex of mice used in the research is not stated anywhere in the article. Explain why this information is relevant and should have been included.
7.14 What electrical changes occur in muscles as they get tired? Student subjects hold their arms above their shoulders until they drop. Meanwhile, the electrical activity in their arm muscles is measured. This is
a. an observational study.
b. an uncontrolled experiment.
c. a randomized comparative experiment.
7.15 Can changing a person’s diet reduce high blood pressure? Vegetarian diets and low-salt diets are both promising alternatives. Men with high blood pressure are assigned at random to four diets: (1) normal diet with unrestricted salt, (2) vegetarian diet with unrestricted salt, (3) normal diet with restricted salt, and (4) vegetarian diet with restricted salt. This experiment has
a. one factor—the choice of diet.
b. two factors—normal/vegetarian diet and unrestricted/restricted salt.
c. four factors—the four diets being compared.
7.16 The response variable in the experiment described in Exercise 7.15 is
a. the amount of salt in the subject’s diet.
b. which of the four diets a subject is assigned to.
c. change in blood pressure after 8 weeks on the assigned diet.
7.27 Does regular exercise reduce the risk of a heart attack? Here are two ways to study this question. Explain clearly why the second design will produce more trustworthy data.
a. A researcher finds 2000 men older than age 40 who exercise regularly and have not had heart attacks. She matches each with a similar man who does not exercise regularly, and she follows both groups for five years.
b. Another researcher finds 4000 men older than age 40 who have not had heart attacks and are willing to participate in a study. She assigns 2000 of the men to a regular program of supervised exercise. The other 2000 continue their usual habits. The researcher follows both groups for five years.
7.36 Fractures of the spine are common and serious among women with advanced osteoporosis (low mineral density in the bones). Can taking strontium renelate help? A large medical trial assigned 1649 women to take either strontium renelate or a placebo each day. All the subjects had osteoporosis and had suffered at least one fracture. All were taking calcium supplements and receiving standard medical care. The response variables were measurements of bone density and counts of new fractures over three years. The subjects were treated at 10 medical centers, each in a different country. Outline a block design for this experiment, with the medical centers as blocks. Explain why this is the proper design.

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