The Community Intervention Trial for Smoking Cessation asked whether acommunity-wide

Internet telephone calls. You can use your computer to make long-distance telephone calls over the Internet. How will the cost affect the use of this service? A university plans an experiment to find out. It will offer voice over Internet service to all 350 students in one of its dormitories. Some students will pay a low flat rate. Others will pay higher rates at peak periods and very low rates off-peak. The university is interested in how the payment plan affects the amount and time of use. What are the subjects, the factors, the treatments, and the response variables in this experiment?

Growing in the shade. Ability to grow in shade may help pines found in the dry forests of Arizona resist drought. How well do these pines grow in shade? Investigators planted pine seedlings in a greenhouse in either full light, light reduced to 25% of normal by shade cloth, or light reduced to 5% of normal. At the end of the study, they dried the young trees and weighed them. What are the individuals, the treatments, and the response variable in this experiment?

Improving adolescents habits. Most American adolescents dont eat well and dont exercise enough. Can middle schools increase physical activity among their students? Can they persuade students to eat better? Investigators designed a physical activity intervention to increase activity in physical education classes and during leisure periods throughout the school day. They also designed a nutrition intervention that improved school lunches and offered ideas for healthy home-packed lunches. Each participating school was randomly assigned to one of the interventions, both interventions, or no intervention. The investigators observed physical activity and lunchtime consumption of fat. Identify the individuals, the factors, and the response variables in this experiment. Use a diagram like that in Figure 9.1 to display the treatments.

Reducing unemployment. Will cash bonuses speed the return to work of unemployed people? A state department of employment security notes that last year 68% of people who filed claims for unemployment insurance found a new job within 15 weeks. As an experiment, the state offers $500 to people filing unemployment claims if they find a job within 15 weeks. The percent who do so increases to 77%. Explain why confounding with lurking variables makes it impossible to say whether the treatment really caused the increase.

Does ginkgo improve memory? The law allows marketers of herbs and other natural substances to make health claims that are not supported by evidence. Brands of ginkgo extract claim to improve memory and concentration. A randomized comparative experiment found no evidence for such effects.3 The subjects were 230 healthy people over 60 years old. They were randomly assigned to ginkgo or a placebo pill (a dummy pill that looks and tastes the same). All the subjects took a battery of tests for learning and memory before treatment started and again after six weeks. (a) Following the model of Figure 9.3, outline the design of this experiment. (b) Use the Simple Random Sample applet, other software, or Table B to assign half the subjects to the ginkgo group. If you use software, report the first 20 members of the ginkgo group (in the applets Sample bin) and the first 20 members of the placebo group (those left in the Population hopper). If you use Table B, start at line 103 and choose only the first 5 members of the ginkgo group.

Can tea prevent cataracts? Eye cataracts are responsible for over 40% of blindness around the world. Can drinking tea regularly slow the growth of cataracts? We cant experiment on people, so we use rats as subjects. Researchers injected 18 young rats with a substance that causes cataracts. One group of the rats also received black tea extract; a second group received green tea extract; and a third got a placebo, a substance with no effect on the body. The response variable was the growth of cataracts over the next six weeks. Yes, both tea extracts did slow cataract growth.4 (a) Following the model of Figures 9.3 and 9.4, outline the design of this experiment. (b) The Simple Random Sample applet allows you to randomly assign subjects to APPLET more than two groups. Use the applet to choose an SRS of 6 of the 18 rats to form the first group. Which rats are in this group? The Population hopper now contains the 12 remaining rats, in scrambled order. Click Sample again to choose an SRS of 6 of these to make up the second group. Which rats were chosen? The 6 rats remaining in the Population hopper form the third group.

Growing in the shade. You have 45 pine seedlings available for the experiment described in Exercise 9.2. Outline the design of this experiment. Use software or Table B to randomly assign seedlings to the three treatment groups.

Conserving energy. Example 9.5 describes an experiment to learn whether providing households with electronic meters or charts will reduce their electricity consumption. An executive of the electric company objects to including a control group. He says: It would be simpler to just compare electricity use last year (before the meter or chart was provided) with consumption in the same period this year. If households use less electricity this year, the meter or chart must be working. Explain clearly why this design is inferior to that in Example 9.5.

Exercise and heart attacks. 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. 1. A researcher finds 2000 men over 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 5 years. 2. Another researcher finds 4000 men over 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 5 years.

The Monday effect. Puzzling but true: stocks tend to go down on Mondays. There is no convincing explanation for this fact. A study looked at this Monday effect in more detail, using data on the daily returns of stocks over a 30-year period. Here are some of the findings:

Dealing with pain. Health care providers are giving more attention to relieving the pain of cancer patients. An article in the journal Cancer surveyed a number of studies and concluded that controlled-release morphine tablets, which release the painkiller gradually over time, are more effective than giving standard morphine when the patient needs it.6 The methods section of the article begins: Only those published studies that were controlled (i.e., randomized, double blind, and comparative), repeated-dose studies with CR morphine tablets in cancer pain patients were considered for this review. Explain the terms in parentheses to someone who knows nothing about medical experiments.

Does meditation reduce anxiety? An experiment that claimed to show that meditation reduces anxiety proceeded as follows. The experimenter interviewed the subjects and rated their level of anxiety. Then the subjects were randomly assigned to two groups. The experimenter taught one group how to meditate and they meditated daily for a month. The other group was simply told to relax more. At the end of the month, the experimenter interviewed all the subjects again and rated their anxiety level. The meditation group now had less anxiety. Psychologists said that the results were suspect because the ratings were not blind. Explain what this means and how lack of blindness could bias the reported results.

Comparing hand strength. Is the right hand generally stronger than the left in right-handed people? You can crudely measure hand strength by placing a bathroom scale on a shelf with the end protruding, then squeezing the scale between the thumb below and the four fingers above it. The reading of the scale shows the force exerted. Describe the design of a matched pairs experiment to compare the strength of the right and left hands, using 10 right-handed people as subjects. (You need not actually do the randomization.)

How long did I work? A psychologist wants to know if the difficulty of a task influences our estimate of how long we spend working at it. She designs two sets of mazes that subjects can work through on a computer. One set has easy mazes and the other has hard mazes. Subjects work until told to stop (after 6 minutes, but subjects do not know this). They are then asked to estimate how long they worked. The psychologist has 30 students available to serve as subjects. (a) Describe the design of a completely randomized experiment to learn the effect of difficulty on estimated time.

Technology for teaching statistics. The Brigham Young University statistics department is performing randomized comparative experiments to compare teaching methods. Response variables include students final-exam scores and a measure of their attitude toward statistics. One study compares two levels of technology for large lectures: standard (overhead projectors and chalk) and multimedia. The individuals in the study are the 8 lectures in a basic statistics course. There are four instructors, each of whom teaches two lectures. Because the lecturers differ, their lectures form four blocks.8 Suppose the lectures and lecturers are as follows: Lecture Lecturer Lecture Lecturer 1 Hilton 5 Tolley 2 Christensen 6 Hilton 3 Hadfield 7 Tolley 4 Hadfield 8 Christensen Outline a block design and do the randomization that your design requires.

A study of cell phones and the risk of brain cancer looked at a group of 469 people who have brain cancer. The investigators matched each cancer patient with a person of the same sex, age, and race who did not have brain cancer, then asked about use of cell phones. This is (a) an observational study. (b) an uncontrolled experiment. (c) a randomized comparative experiment.

What electrical changes occur in muscles as they get tired? Student subjects hold their arms above their shoulders until they have to drop them. 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.

Can changing diet reduce high blood pressure? Vegetarian diets and low-salt diets are both promising. Men with high blood pressure are assigned at random to four diets: (1) normal diet with unrestricted salt; (2) vegetarian with unrestricted salt; (3) normal with restricted salt; and (4) vegetarian 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.

In the experiment of the previous exercise, the 240 subjects are labeled 001 to 240. Software assigns an SRS of 60 subjects to Diet 1, an SRS of 60 of the remaining 180 to Diet 2, and an SRS of 60 of the remaining 120 to Diet 3. The 60 who are left get Diet 4. This is a (a) completely randomized design. (b) block design, with four blocks. (c) matched pairs design.

An important response variable in the experiment described in Exercise 9.18 must be (a) the amount of salt in the subjects diet. (b) which of the four diets a subject is assigned to. (c) change in blood pressure after 8 weeks on the assigned diet.

A medical experiment compares an antidepression medicine with a placebo for relief of chronic headaches. There are 36 headache patients available to serve as subjects. To choose 18 patients to receive the medicine, you would (a) assign labels 01 to 36 and use Table B to choose 18. (b) assign labels 01 to 18, because only 18 need be chosen. (c) assign the first 18 who signed up to get the medicine.

The Community Intervention Trial for Smoking Cessation asked whether a community-wide advertising campaign would reduce smoking. The researchers located 11 pairs of communities, each pair similar in location, size, economic status, and so on. One community in each pair participated in the advertising campaign and the other did not. This is (a) an observational study. (b) a matched pairs experiment. (c) a completely randomized experiment.

To decide which community in each pair in the previous exercise should get the advertising campaign, it is best to (a) toss a coin. (b) choose the community that will help pay for the campaign. (c) choose the community with a mayor who will participate.

A marketing class designs two videos advertising an expensive Mercedes sports car. They test the videos by asking fellow students to view both (in random order) and say which makes them more likely to buy the car. Mercedes should be reluctant to agree that the video favored in this study will sell more cars because (a) the study used a matched pairs design instead of a completely randomized design. (b) results from students may not generalize to the older and richer customers who might buy a Mercedes. (c) this is an observational study, not an experiment.

Wine, beer, or spirits? Example 8.2 (page 191) describes a study that compared three groups of people: the first group drinks mostly wine, the second drinks mostly beer, and the third drinks mostly spirits. This study is comparative, but it is not an experiment. Why not?

Treating breast cancer. The most common treatment for breast cancer discovered in its early stages was once removal of the breast. It is now usual to remove only the tumor and nearby lymph nodes, followed by radiation. To study whether these treatments differ in their effectiveness, a medical team examines the records of 25 large hospitals and compares the survival times after surgery of all women who have had either treatment. (a) What are the explanatory and response variables? (b) Explain carefully why this study is not an experiment. (c) Explain why confounding will prevent this study from discovering which treatment is more effective. (The current treatment was in fact recommended after several large randomized comparative experiments.)

Wine, beer, or spirits? You have recruited 300 adults aged 45 to 65 who are willing to follow your orders about alcohol consumption over the next five years. You want to compare the effects on heart disease of moderate drinking of just wine, just beer, or just spirits. Outline the design of a completely randomized experiment to do this. (No such experiment has been done because subjects arent willing to have their drinking regulated for years.)

Marijuana and work. How does smoking marijuana affect willingness to work? Canadian researchers persuaded young adult men who used marijuana to live for 98 days in a “planned environment”. The men earned money by weaving belts. They used their earnings to pay for meals and other consumption and could keep any money left over. One group smoked two potent marijuana cigarettes every evening. The other group smoked two weak marijuana cigarettes. All subjects could buy more cigarettes but were given strong or weak cigarettes depending on their group. Did the weak and strong groups differ in work output and earnings? (a) Outline the design of this experiment. (b) Here are the names of the 20 subjects. Use software or Table B at line 131 to carry out the randomization your design requires.

The benefits of red wine. Does red wine protect moderate drinkers from heart disease better than other alcoholic beverages? Red wine contains substances called polyphenols that may change blood chemistry in a desirable way. This calls for a randomized comparative experiment. The subjects were healthy men aged 35 to 65. They were randomly assigned to drink red wine (9 subjects), drink white wine (9 subjects), drink white wine and also take polyphenols from red wine (6 subjects), take polyphenols alone (9 subjects), or drink vodka and lemonade (6 subjects).10 Outline the design of the experiment and randomly assign the 39 subjects to the 5 groups. If you use Table B, start at line 107.

Response to TV ads. You decide to use a completely randomized design in the two-factor experiment on response to advertising described in Example 9.2 (page 214). The 36 students named below will serve as subjects. (Ignore the asterisks.) Outline the design and randomly assign the subjects to the 6 treatments. If you use Table B, start at line 130. Alomar Denman Han Liang Padilla Valasco Asihiro Durr Howard Maldonado Plochman Vaughn Bennett Edwards Hruska Marsden Rosen Wei Bikalis Farouk Imrani Montoya Solomon Wilder Chao Fleming James OBrian Trujillo Willis Clemente George Kaplan Ogle Tullock Zhang

Improving adolescents habits. Twenty-four public middle schools agree to participate in the experiment described in Exercise 9.3 (page 215). Use a diagram to outline a completely randomized design for this experiment. Do the randomization required to assign schools to treatments. If you use the Simple Random Sample applet or other software, choose all four treatment groups. If you use Table B, start at line 105 and choose only the first two groups.

Relieving headaches. Doctors identify chronic tensiontype 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? (a) Use a diagram like Figure 9.1 to display the treatments in a design with two factors: medication, yes or no and stress management, yes or no. Then outline the design of a completely randomized experiment to compare these treatments. (b) The headache sufferers named below have agreed to participate in the study. Randomly assign the subjects to the treatments. If you use the Simple Random Sample applet or other software, assign all the subjects. If you use Table B, start at line 130 and assign subjects to only the first treatment group. Abbott Decker Herrera Lucero Richter Abdalla Devlin Hersch Masters Riley Alawi Engel Hurwitz Morgan Samuels Broden Fuentes Irwin Nelson Smith Chai Garrett Jiang Nho Suarez Chuang Gill Kelley Ortiz Upasani Cordoba Glover Kim Ramdas Wilson Custer Hammond Landers Reed Xiang

Fabric finishing. A maker of fabric for clothing is setting up a new line to finish the raw fabric. The line will use either metal rollers or natural-bristle rollers to raise the surface of the fabric; a dyeing cycle time of either 30 minutes or 40 minutes; and a temperature of either 150C or 175C. An experiment will compare all combinations of these choices. Three specimens of fabric will be subjected to each treatment and scored for quality. (a) What are the factors and the treatments? How many individuals (fabric specimens) does the experiment require? (b) Outline a completely randomized design for this experiment. (You need not actually do the randomization.)

Frappuccino light? Heres the opening of a press release from June 2004: Starbucks Corp. on Monday said it would roll out a line of blended coffee drinks intended to tap into the growing popularity of reduced-calorie and reduced-fat menu choices for Americans. You wonder if Starbucks customers like the new Mocha Frappuccino Light as well as the regular Mocha Frappuccino coffee. (a) Describe a matched pairs design to answer this question. Be sure to include proper blinding of your subjects. (b) You have 20 regular Starbucks customers on hand. Use the Simple Random Sample applet or Table B at line 141 to do the randomization that your design requires.

Growing trees faster. The concentration of carbon dioxide (CO2) in the atmosphere is increasing rapidly due to our use of fossil fuels. Because green plants use CO2 to fuel photosynthesis, more CO2 may cause trees to grow faster. An elaborate apparatus allows researchers to pipe extra CO2 to a 30-meter circle of forest. We want to compare the growth in base area of trees in treated and untreated areas to see if extra CO2 does in fact increase growth. We can afford to treat three circular areas.11 (a) Describe the design of a completely randomized experiment using six well-separated 30-meter circular areas in a pine forest. Sketch the circles and carry out the randomization your design calls for. (b) Areas within the forest may differ in soil fertility. Describe a matched pairs design using three pairs of circles that will reduce the extra variation due to different fertility. Sketch the circles and carry out the randomization your design calls for.

Athletes taking oxygen. We often see players on the sidelines of a football game inhaling oxygen. Their coaches think this will speed their recovery. We might measure recovery from intense exertion as follows: Have a football player run 100 yards three times in quick succession. Then allow three minutes to rest before running 100 yards again. Time the final run. Because players vary greatly in speed, you plan a matched pairs experiment using 25 football players as subjects. Discuss the design of such an experiment to investigate the effect of inhaling oxygen during the rest period.

Protecting ultramarathon runners. An ultramarathon, as you might guess, is a footrace longer than the 26.2 miles of a marathon. Runners commonly develop respiratory infections after an ultramarathon. Will taking 600 milligrams of vitamin C daily reduce these infections? Researchers randomly assigned ultramarathon runners to receive either vitamin C or a placebo. Separately, they also randomly assigned these treatments to a group of nonrunners the same age as the runners. All subjects were watched for 14 days after the big race to see if infections developed.12 (a) What is the name for this experimental design? (b) Use a diagram to outline the design.

Reducing spine fractures. 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 experiment assigned 1649 women to take either strontium renelate or a placebo each day. All of 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 in 10 different countries.13 Outline a block design for this experiment, with the medical centers as blocks. Explain why this is the proper design.

Wine, beer, or spirits? Women as a group develop heart disease much later than men. We can improve the completely randomized design of Exercise 9.27 by using women and men as blocks. Your 300 subjects include 120 women and 180 men. Outline a block design for comparing wine, beer, and spirits. Be sure to say how many subjects you will put in each group in your design.

Response to TV ads, continued. We can improve on the completely randomized design you outlined in Exercise 9.30. The 36 subjects include 24 women and 12 men. Men and women often react differently to advertising. You therefore decide to use a block design with the two genders as blocks. You must assign the 6 treatments at random within each block separately. (a) Outline the design with a diagram. (b) The 12 men are marked with asterisks in the list in Exercise 9.30. Use Table B, beginning at line 140, to do the randomization. Report your result in a table that lists the 24 women and 12 men and the treatment you assigned to each.

Prayer and meditation. You read in a magazine that nonphysical treatments such as meditation and prayer have been shown to be effective in controlled scientific studies for such ailments as high blood pressure, insomnia, ulcers, and asthma. Explain in simple language what the article means by controlled scientific studies. Why can such studies in principle provide good evidence that, for example, meditation is an effective treatment for high blood pressure?

College students. Give an example of a question about college students, their behavior, or their opinions that would best be answered by (a) a sample survey. (b) an experiment.

Quick randomizing. Heres a quick and easy way to randomize. You have 100 subjects, 50 women and 50 men. Toss a coin. If its heads, assign the men to the treatment group and the women to the control group. If the coin comes up tails, assign the women to treatment and the men to control. This gives every individual subject a 50-50 chance of being assigned to treatment or control. Why isnt this a good way to randomly assign subjects to treatment groups?

Daytime running lights. Canada requires that cars be equipped with daytime running lights,headlights that automatically come on at a low level when the car is started. Many manufacturers are now equipping cars sold in the United States with running lights. Will running lights reduce accidents by making cars more visible? (a) Briefly discuss the design of an experiment to help answer this question. In particular, what response variables will you examine? (b) Example 9.7 (page 223) discusses center brake lights. What cautions do you draw from that example that apply to an experiment on the effects of running lights?

Do antioxidants prevent cancer? People who eat lots of fruits and vegetables have lower rates of colon cancer than those who eat little of these foods. Fruits and vegetables are rich in antioxidants such as vitamins A, C, and E. Will taking antioxidants help prevent colon cancer? A medical experiment studied this question with 864 people who were at risk of colon cancer. The subjects were divided into four groups: daily beta-carotene, daily vitamins C and E, all three vitamins every day, or daily placebo. After four years, the researchers were surprised to find no significant difference in colon cancer among the groups.14 (a) What are the explanatory and response variables in this experiment? (b) Outline the design of the experiment. Use your judgment in choosing the group sizes. (c) The study was double-blind. What does this mean? (d) What does no significant difference mean in describing the outcome of the study? (e) Suggest some lurking variables that could explain why people who eat lots of fruits and vegetables have lower rates of colon cancer. The experiment suggests that these variables, rather than the antioxidants, may be responsible for the observed benefits of fruits and vegetables.

An herb for depression? Does the herb Saint-Johns-wort relieve major depression? Here are some excerpts from the report of a study of this issue.15 The study concluded that the herb is no more effective than a placebo. (a) Design: Randomized, double-blind, placebo-controlled clinical trial. . . . A clinical trial is a medical experiment using actual patients as subjects. Explain the meaning of each of the other terms in this description. (b) Participants...were randomly assigned to receive either Saint-Johns-wort extract (n = 98) or placebo (n = 102). . . . The primary outcome measure was the rate of change in the Hamilton Rating Scale for Depression over the treatment period. Based on this information, use a diagram to outline the design of this clinical trial.

Explaining medical research. Observational studies had suggested that vitamin E reduces the risk of heart disease. Careful experiments, however, showed that vitamin E has no effect, at least for women. According to a commentary in the Journal of the American Medical Association: Thus, vitamin E enters the category of therapies that were promising in epidemiologic and observational studies but failed to deliver in adequately powered randomized controlled trials. As in other studies, the healthy user bias must be considered, ie, the healthy lifestyle behaviors that characterize individuals who care enough about their health to take various supplements are actually responsible for the better health, but this is minimized with the rigorous trial design.16 A friend who knows no statistics asks you to explain this. (a) What is the difference between observational studies and experiments? (b) What is a randomized controlled trial? (Well discuss adequately powered in Chapter 16.) (c) How does healthy user bias explain how people who take vitamin E supplements have better health in observational studies but not in controlled experiments?

Randomization avoids bias. Suppose that the 25 even-numbered students APPLET among the 50 students available for the comparison of on-campus and online instruction (Example 9.4) are older, employed students. We hope that randomization will distribute these students roughly equally between the on-campus and online groups. Use the Simple Random Sample applet to take 20 samples of size 25 from the 50 students. (Be sure to click Reset after each sample.) Record the counts of even-numbered students in each of your 20 samples. You see that there is considerable chance variation but no systematic bias in favor of one or the other group in assigning the older students. Larger samples from a larger population will on the average do an even better job of creating two similar groups.