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Mind On Statistics 4th Edition David D Busch, Jessica M Utts, Robert F Heckard - Solutions

Explain why confounding variables are more of a problem in observational studies than in randomized experiments.Give an example.
Refer to Exercise 6.27, in which three randomized experiments are described. In each case, explain the extent to which you think the results from the sample in the experiment could be extended to a larger population.
Explain whether a variable can be:a. Both a confounding variable and a lurking variable.b. Both a response variable and a confounding variable.c. Both an explanatory variable and a dependent variable.
Give an example of an observational study, and explain the difference between a confounding variable and a lurking variable in the context of your example.
Refer to Example 6.6 (p. 208), “Dull Rats,” which was done by using a completely randomized design.a. What were the treatments in this experiment?b. Were the experimental units the 60 individual rats or the 12 individual experimenters? Explain.c. Explain how the experiment could have been done
A study was done (fictional) to compare the proportion of children who developed myopia after sleeping with and without a nightlight. The study found that the results differed based on whether at least one parent suffered from myopia by age 20. The percents of children suffering from myopia were as
Explain whether it is possible for a variable to be both a confounding variable and an interacting variable.
Refer to Case Study 1.6, in which physicians were randomly assigned to take aspirin or a placebo, and heart attack rates were compared. Draw a figure similar to one of Figures 6.2 through 6.5 that illustrates the steps for Case Study 1.6.
Refer to the study in Example 6.8 that compares ages at death for left-handed and right-handed people. Draw a figure similar to one of Figures 6.2 through 6.5 that illustrates the steps for Example 6.8.
Refer to Exercise 6.81 and answer these questions.a. For each study, on the basis of the information given, is it clearly a randomized experiment? If not, explain what additional information would make it clear that the study was a randomized experiment rather than an observational study.b. For
Specify what an individual “unit” is in each of the following studies. Then specify what two variables were measured on each unit.a. A study found that tomato plants raised in full sunlight produced more tomatoes than did tomato plants raised in partial shade.b. A study found that gas mileage
Find an example of a randomized experiment in the news.Answer the following questions about it. Be sure to include the news article with your response.a. What are the explanatory and response variables? What relationship was found, if any?b. What treatments were assigned? Was a control group or
Is it possible for each of the following to be used in the same study (on the same units)? Explain or give an example of such a study.a. A placebo and a double-blind procedure.b. A matched-pair design and a retrospective study.c. A case–control study and random assignment of treatments.
Find an example of an observational study in the news.Answer the following questions about it. Be sure to include the news article with your response.a. What are the explanatory and response variables, or is this distinction not possible?b. Briefly describe how the study was done. For instance, was
Refer to Case Study 6.2 (p. 195), “Kids and Weight Lifting.”Did the experiment described there use a completely randomized design, a matched-pair design, or a randomized block design? Explain.
Refer to the study reported in Example 2.2, relating the use of nightlights in childhood and the incidence of subsequent myopia.a. Was the research based on an observational study or a randomized experiment? Explain.b. Which one of the “difficulties and disasters” in Section 6.4 do you think is
In this chapter, you learned that cause and effect can be concluded from randomized experiments but generally not from observational studies. Why don’t researchers simply conduct all studies as randomized experiments rather than observational studies?
Refer to Example 6.3 in which children were randomly assigned to three treatment groups. Suppose now that 60 children will be randomly assigned to these three groups.Describe how you could carry out the random assignments.
The article also reported that “contrary to popular belief men’s self-esteem may take a greater licking than women’s when their hair just won’t behave. Men were likely to feel?
Discuss each of the following “difficulties and disasters” in the context of this research.a. Ecological validity.b. Extending results inappropriately.c. Experimenter effect.
Discuss whether this study could have been blind or doubleblind, and whether you think it was blind or double-blind.
What were the explanatory and response variables for this study? Were they categorical variables or quantitative variables?
Was this an observational study or a randomized experiment? Explain.
Another drawback of the study quoted in the Sacramento Bee was that “people who develop breast cancer are much more likely to remember whether they took hormones compared to women who don’t develop the disease.” Which of the “difficulties and disasters” in Section 6.4 is represented by
One drawback of the study quoted in the Sacramento Bee was that “the women in the study may not resemble women today, because many women now take lower doses of progestin than was used during the follow-up years of the study (1979–95).” Which of the “difficulties and disasters” in Section
Assuming that the women and their physicians made the decision about which treatment to pursue (combined hormones, estrogen alone, or no hormones), discuss the possibility of confounding variables in this study.
Near the end of the Sacramento Bee article, it was noted that“the NCI researchers analyzed their results by the woman’s weight. . . There was no increased breast cancer risk in heavier women.” Which of the “Difficulties and Disasters” in Section 6.4 is represented by this statement?
To whom are the women taking combined therapy and estrogen alone being compared when the increased risks of 8% and 1% are computed?
What are the explanatory and response variables for this study? Are they quantitative or categorical? If they are categorical, what are the categories?
Discuss whether this research is the following:a. A case–control study.b. A retrospective study or a prospective study?
Do you think this research was an observational study or a randomized experiment? Explain.
Pick the two “difficulties and disasters” that are most likely to be a problem in each of the following studies, and explain why they would be a problem.a. To compare marketing methods, a marketing professor randomly divides a large class into three groups and randomly assigns each group to
A categorical interacting variable defines subgroups for which the effect of the explanatory variable on the outcome variable differs. For instance, as explained in the text, for the nicotine patch experiment described in Case Study 6.3, one interacting variable was whether or not there were other
Refer to Exercise 6.57, describing a case–control study relating childhood diet and heart disease. Comment on the extent to which each of the following is likely to be a problem.a. Confounding variables and the implication of causation in observational studies.b. Extending results
Pick the two “difficulties and disasters” that are most likely to be a problem in the following study, and explain why each would be a problem: A researcher at a large medical clinic wants to determine whether a high-fat diet in childhood is more likely to result in heart disease in later life.
Is the experimenter effect more likely to be a problem in a study that is double-blind, single-blind, or not blind at all?Explain.
Refer to Exercise 6.27, in which three randomized experiments are described. For each of the experiments described, pick one of the “difficulties and disasters” described in Section 6.4, and explain how it might be a problem in that experiment.
Refer to Exercise 6.41, describing a study about pet ownership and marriage. Explain whether each of the following is likely to be a problem for that study:a. Confounding variables and the implication of causation in observational studies.b. Hawthorne and experimenter effects.c. Ecological validity
A retrospective study of 517 veterans who never smoked was done to determine whether there was an association between lung disease and exposure to workplace gases, dust, and fumes (Clawson, Stanford Report, November 1, 2000).In this study, subjects were asked whether or not they remembered being
In a sample of 500 college students aged 18 to 21, it was found that offering discount coupons for restaurant meals substantially increased the likelihood that the students would eat at those restaurants. Explain how “extending results inappropriately” may be a problem in the interpretation of
An experiment on elephants in captivity was done to find out whether breeding would occur more often when the elephants were kept together in a herd or when a male was isolated with a female. Explain how ecological validity affects the ability to generalize these results to wild elephants.
An investigator believes that a new medication will help to reduce anxiety and that a placebo will not. In a single-blind study (patients are blind), she finds that the group taking the new medication had reduced anxiety while the placebo group did not. Explain how the experimenter effect may have
In a study on worker productivity done in 1927 in Cicero, Illinois, it was observed that productivity improved when the lighting was increased. However, it was observed that productivity also improved when the lighting was decreased.What term is used to describe the fact that productivity in
A new medication is observed to cause a weight loss in women but a weight gain in men. Identify what the response variable, explanatory variable, and interacting variable are in this situation.
Researchers have found that women who take oral contraceptives (birth control pills) are at higher risk of having a heart attack or stroke and that the risk is substantially higher if a woman smokes. In investigating the relationship between taking oral contraceptives (the explanatory variable)and
For each of the following, explain whether the study summary describes an interacting variable or a confounding variable.a. A comparison of the mean grade point averages of male and female students finds more difference for fraternity and sorority members than for students who are not fraternity
This is also Exercise 1.25. An article in Science magazine(Service, 1994) discussed a study comparing the health of 6000 vegetarians and a similar number of their friends and relatives who were not vegetarians. The vegetarians had a 28% lower death rate from heart attacks and a 39% lower death rate
This is also Exercise 1.38. A headline in a major newspaper read, “Breast-Fed Youth Found to Do Better in School.”a. Do you think this statement was based on an observational study or a randomized experiment? Explain.b. Given your answer in part (a), which of these two alternative headlines do
Explain why it is preferable, whenever possible, to conduct a randomized experiment rather than an observational study.
Reuters (June 24, 1997) reported on a study published in the Journal of the American Medical Association (1997, vol. 277, pp. 1940–1944) in which researchers recruited 276 volunteers (aged 18 to 55) and used nose drops to infect them with a cold virus. The volunteers were then quarantined and
A story at ABCNews.com (“Pet Contact” by Rita Rubin, March 17, 1998) reported that Karen Allen, a researcher at the University of Buffalo, found that couples who own cats or dogs have more satisfying marriages and are less stressed out than those who don’t own pets. Pet owners also have more
Find an example of an observational study in the news.Determine whether or not it was a case–control study and whether it was prospective or retrospective. Specify the explanatory and response variables, and explain whether confounding variables were likely to be a major problem in interpreting
A study will be done to determine the relationship, if any, between where a college student lives (on-campus or offcampus) and grade point average. Would it be better to use a randomized experiment or an observational study?Explain.
Suppose researchers were interested in determining the relationship, if any, between the use of cellular telephones and the incidence of brain cancer. Would it be better to use a randomized experiment, a case–control study, or an observational study that did not use cases and controls? Explain.
A medical researcher wants to know how lifetime sun exposure affects the risk of skin cancer for persons over 50 years old. Describe how data might be collected for a retrospective case–control study /?
Students who had meningitis were matched with students without meningitis using sex, undergraduate (or graduate)status, and college. The students’ recent activities were examined to discover risk factors for meningitis. Explain whether each of the following terms applies to this observational
Students whose undergraduate major was economics were followed for 10 years after graduation to study the number of different jobs they took. Explain whether each of the following terms applies to this observational study.a. Prospective study.b. Retrospective study.c. Case–control study.
Suppose you want to know whether men or women spend more time talking on a cell phone during a week’s time.a. Describe how you would collect the data in a retrospective observational study.b. Describe how you would collect the data in a prospective observational study.c. Refer to parts (a) and
A teacher wants to determine how class attendance during the term affects grades on the final exam.a. Describe how the data would be collected in a prospective observational study.b. Describe how the data would be collected in a retrospective observational study.c. Refer to parts (a) and (b). Give
Echinacea is an herb that may help to prevent colds and flu. Explain how researchers could conduct a double-blind, double-dummy experiment to compare echinacea tea with chewable vitamin C pills for effectiveness in preventing colds.
Refer to Exercise 6.27. In each case, explain whether a control group was used and whether a placebo treatment was used.
Refer to Exercise 6.27. In each case, explain whether the experiment was a matched-pair design, a block design, or neither.
Refer to Exercise 6.27. In each case, designate the explanatory variable and the response variable.
A fast-food chain sells its burgers alone or as part of a “value meal” that includes fries and a drink. They know that some customers are health-conscious. They want to do an experiment to determine whether the proportion of customers choosing the meal would increase if they offered baby
Explain whether each of the following experiments was single-blind, double-blind, or neither.a. An electric company wanted to know whether residential customers would use less electricity during peak hours if they were charged more during those hours. One hundred customers were randomly selected to
Refer to Case Study 6.3 (p. 199), “Quitting Smoking with Nicotine Patches,” which used a completely randomized design. Explain how the experiment could have been done by using a randomized block design instead.
One hundred volunteers agree to participate in an experiment. There are four treatments, each of which will be assigned to 25 participants. Using Example 6.3 (p. 197) for guidance, explain how you could use statistical software such as Minitab to randomly assign participants to treatments.
A school district has 20 elementary schools, and each school has 12 classes that can be used for a study.a. Using schools as blocks, describe a randomized block design to compare three teaching methods.b. Explain why schools should be used as blocks.
Twenty volunteers aged 40 to 65 years old will participate in an experiment to compare two methods of memorizing information. The age variation in the participants concerns the researchers because memorization skills decrease with age.a. Describe how the study could be done using a matchedpair
Researchers want to design a study to compare topical cream (applied to the skin) and a drug taken in capsule form for the treatment of a certain type of skin rash. Sixty volunteers who have the rash agree to participate in the study.a. If each volunteer is given only one treatment, can the study
Twenty grocery stores will participate in an experiment to compare the effectiveness of two methods for displaying a product. The response variable will be the number of items of the product sold during a 1-week period.a. Describe a completely randomized design for this experiment.b. Describe a
Case Study 6.3. (p. 199) was about an experiment done to determine whether nicotine patches helped smokers to quit smoking. For that experiment, draw a figure similar to Figure 6.3 (p. 195) illustrating the steps of the study.
Twenty students agreed to participate in a study on colds.Ten were randomly assigned to receive vitamin C, and the remaining 10 received a tablet that looked and tasted like vitamin C but in fact contained only sugar and flavoring.The students did not know whether they were taking vitamin C or not,
Two weight-training regimens designed to improve arm strength will be compared. The response variable will be the improvement in arm strength at the end of six weeks of training. Forty individuals—20 males and 20 females—will participate in the study.a. Describe how a completely randomized
Suppose that we want to determine whether people who want to lose weight would lose more in three months by dieting or by exercising. Sixty people have volunteered to participate. Briefly describe how a randomized experiment would be done in this situation.
An experiment will be done to determine whether college students learn information better when listening to rap music, when listening to classical music, or when not listening to music. In the study, each participant will read a chapter from a history textbook and then take a test about the
Case Study 1.5. in Chapter 1 was about the association between blood pressure and frequency of participating in religious activities. Why was this study conducted as an observational study instead of an experiment?
(p. 194), illustrating the steps in this study.
A news article on the Reuters Health website, December 18, 1998, reported that:A study of over 1200 people over age 65 showed that the“owls”—those who go to sleep after 11 p.m. and rise after 8 a.m.—tend to be as healthy and intelligent as “larks”—those who go to bed before 11 p.m.
A news article by Reuters on October 6, 1998, reported:In a new study, Dr. Matti Uhari and colleagues at the University of Oulu in Finland randomly gave 857 healthy children in daycare centers xylitol in syrup, gum, or a lozenge form, or a placebo gum or syrup in five doses per day for 3 months.
For the research scenarios in parts (a) and (b), explain whether a randomized experiment could be used.a. To compare two programs to reduce the number of commuters who drive to work: providing discount coupons for the bus, or providing shuttle service for people who need to run errands during the
For the research scenarios in parts (a) and (b), explain whether a randomized experiment could be used.a. To study the relationship between long-term practice of meditation and blood pressure.b. To determine whether a special training program improves scores on a standard college admissions test.c.
This is also Exercise 1.14. For each of the studies described, explain whether the study was an observational study or a randomized experiment.a. A group of 100 students was randomly divided, with 50 assigned to receive vitamin C and the remaining 50 to receive a placebo, to determine whether
Specify what an individual unit is in each of the following studies. Then specify what two variables were measured on each unit.a. A study finds that college students who often procrastinate tend to be sick more often than students who do not procrastinate.b. A study finds that sport utility
Remember that a confounding variable affects the response variable and is related to the explanatory variable. For each of the following situations, explain how the given confounding variable meets these criteria.a. Response variable 5 Child’s IQ at age 10; explanatory variable 5 whether mother
This is also Exercise 1.13. For each of the examples given here, decide whether the study was an observational study or a randomized experiment.a. A group of students who were enrolled in an introductory statistics course were randomly assigned to take a web-based course or to take a traditional
This is also Exercise 1.16. Suppose that an observational study showed that students who got at least seven hours of sleep performed better on exams than students who didn’t.Which of the following are possible confounding variables, and which are not? Explain why in each case.a. Number of courses
Remember that a confounding variable affects the response variable and is related to the explanatory variable. For each of the following situations, explain how the given confounding variable meets these criteria.a. Response variable 5 Math skills of children aged 6 to 12 years old; explanatory
Suppose that a statistics teacher wants to know whether the number of hours students spend studying in a group affects the final course grade. In each part, explain whether the research method described is a randomized experiment or an observational study.a. Each student keeps a log of the hours he
Refer to Exercise 6.1. In each part, specify the explanatory variable and the response variable.
In each part, identify the response variable and the explanatory variable in the relationship between the two given variables.a. Daughter’s height and mother’s height.b. Age and weight for children between the ages of 3 and 10 years old.c. Opinion about the death penalty for persons convicted
In each situation, indicate whether you think an observational study or a randomized experiment would be used.Explain why in each case.a. A teacher wants to compare the grade point averages of female students who are in sororities to the grade point averages of female students who are not in
One question asked was as follows: “The term affirmative action has different meanings to different people. Please tell me which statement best describes what you mean by the term: First, affirmative action means granting preferences to women and certain racial and ethnic groups.Second,
Refer to Exercise 5.118. Of the 166 arts and humanities faculty members, 66% favored the policy, while of the 229 engineering, mathematical, and physical sciences faculty, 38%favored it.a. Find the conservative margin of error for the arts and humanities faculty, and use it to compute an
One of the questions asked was, “Do you favor or oppose using race, religion, sex, color, ethnicity, or national origin as a criterion for admission to the University of California?”Of the 804 male respondents, 47% said “Favor,” and of the 197 female respondents, 73% said “Favor.”a.
The article also reported that “among GOP voters, 39 percent give Feinstein high marks.” Would the margin of error accompanying this result be larger, smaller, or the same as the margin of error for the entire sample? Explain.
The report stated that the margin of error was 3.8 percentage points. This value is based on the 642 voters who were considered likely to vote and uses the precise formula you will learn in Chapter 10.a. Compute the conservative margin of error for this poll based on those likely to vote, and
The text of the article said that the 750 adults surveyed were actually 750 registered voters. Based on the information about who was surveyed, if the poll results are to be used to predict the proportion of voters who were likely to vote for Senator Feinstein in November, should the results of all
Read the headline that accompanied the article, which stated that ratings were “up” for both senators. For the June 2000 poll, 57% approved of Feinstein’s performance, compared with 56% and 53%, respectively, for similar polls taken in February 2000 and October 1999. Presumably, the headline
Find an example of a poll that would be considered unscientific because it does not represent a population other than those who responded. Write a few paragraphs describing how the poll was conducted, what was asked, and the results. Explain which of the problems discussed in Sections 5.5 and 5.6

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