Exam 5: Experiments, Good and Bad

Does taking large amounts of vitamins protect against cancer? To study this question, researchers enrolled 29,000 Finnish men, all smokers over the age of 50. Half of the men, selected at random, took vitamin supplements, and others took a dummy pill that has no active ingredient. The researchers followed all the men for eight years. At the end of the study, men in the vitamin group were no less likely to have cancer than men in the other group. This study cast doubt on the popular idea that taking lots of vitamins can reduce the risk of cancer. The study design looked like this: The response variable should be named in the outline at "Question C." The response variable in this study is

Does eating while driving make an accident more likely? Researchers from the National Highway Traffic Safety Administration looked at national traffic and accident records from a recent year for those drivers who were eating versus those who were not. Result: The odds of an accident were 80 percent higher when eating than when not. An example of a lurking variable that might affect the results of this study is:

One method that can be used to avoid problems with confounding variables in observational studies is to

Does taking large amounts of vitamins protect against cancer? To study this question, researchers enrolled 29,000 Finnish men, all smokers over the age of 50. Half of the men, selected at random, took vitamin supplements, and others took a dummy pill that has no active ingredient. The researchers followed all the men for eight years. At the end of the study, men in the vitamin group were no less likely to have cancer than men in the other group. This study cast doubt on the popular idea that taking lots of vitamins can reduce the risk of cancer. The study design looked like this: The method used to form the groups should appear in the outline at the point marked "Question A." What is this method?

Does taking large amounts of vitamins protect against cancer? To study this question, researchers enrolled 29,000 Finnish men, all smokers over the age of 50. Half of the men, selected at random, took vitamin supplements, and others took a dummy pill that has no active ingredient. The researchers followed all the men for eight years. At the end of the study, men in the vitamin group were no less likely to have cancer than men in the other group. This study cast doubt on the popular idea that taking lots of vitamins can reduce the risk of cancer. The study design looked like this: An example of a confounding variable that might affect the results of this study is

A researcher claims that the mean resting pulse rate of all college basketball players in the United States is less than the mean resting pulse rate of all professional basketball players in the United States. The resting pulse rates of a random sample of 115 college basketball players were measured as were the resting pulse rates of a random sample of 80 professional basketball players. The mean resting pulse rates of the two groups were compared. This study is a(n)

Does St. John's wort have a significant effect in treating major depression? A study looked at 340 adult outpatients suffering from major depression as measured by their HAM-D score, randomly assigning each subject to either a placebo, St. John's wort, or a second active treatment for comparison. The study found the difference in treating major depression as measured by improvement in HAM-D scores between St. John's wort and the placebo was not statistically significant. This means that:

A researcher studied whether meeting regularly with a weight-loss counselor helps dieters lose weight. Eighty dieters were available for the study. Half the dieters, assigned at random, received weight-loss counseling. The other half did not. After six months, the weight lost by each dieter was measured. On the average, those who met regularly with a weight-loss counselor lost more weight than those who did not. In order to create groups of subjects that should be similar, on average, in all respects, we use

The article was headlined, "Two Cups of Coffee Can Reduce the Risk of Liver Disease, Study Finds." A meta-analysis, based on combining nine previous studies involving 430,000 individuals, concluded that consumption of two cups of coffee a day reduced the chance of cirrhosis of the liver by 44 percent; even greater consumption was found to further reduce the risk of the disease. The response variable in this study is:

Does taking large amounts of vitamins protect against cancer? To study this question, researchers enrolled 29,000 Finnish men, all smokers over the age of 50. Half of the men, selected at random, took vitamin supplements, and others took a dummy pill that has no active ingredient. The researchers followed all the men for eight years. At the end of the study, men in the vitamin group were no less likely to have cancer than men in the other group. This study cast doubt on the popular idea that taking lots of vitamins can reduce the risk of cancer. The study design looked like this: The statistical name for this study design is

Volunteers for a human performance study were randomly divided into two groups. The first group had their flexibility measured in the morning after a short meditation session while the second group had their flexibility measured in the afternoon with no previous meditation session. The flexibility scores of the two groups were compared. This study is a(n):

A magazine article on preventing cancer says, "Eating one serving of tofu a week may cut your risk of breast cancer 15%, recent research suggests." If 15% is a statistically significant amount, then

A study compares the effect on college students of two different TV advertisements for spring break in Gulf Shores, Alabama. Call the ads "Ad #1" and "Ad #2." We want to know which ad makes more students want to visit Gulf Shores during spring break. The subjects are 90 students taking a course in hotel management. The design of the study looks like this: What is Group 2's treatment (at the point marked "Question B" in the diagram)?

A West Coast university statistics professor wishes to determine which surfboard brand delivers consistently longer rides, Channel Island or JS. He recruits two of his students who surf to assist in an experiment, and the student assigned to the Channel Island board is determined by coin flip. The three head out to the beach for an afternoon, with the professor holding up a sign at random times for the respective student to catch the next wave on his board, and the time spent on that wave is recorded. This is repeated until each student has ridden 10 waves. In the surfing story above, the time spent on the wave is:

Does taking large amounts of vitamins protect against cancer? To study this question, researchers enrolled 29,000 Finnish men, all smokers over the age of 50. Half of the men, selected at random, took vitamin supplements, and others took a dummy pill that has no active ingredient. The researchers followed all the men for eight years. At the end of the study, men in the vitamin group were no less likely to have cancer than men in the other group. This study cast doubt on the popular idea that taking lots of vitamins can reduce the risk of cancer. The study design looked like this: The label for the dummy pill treatment should appear in the outline at the point marked "Question B." What is this label?

A magazine article on preventing cancer says, "Eating one serving of tofu a week may cut your risk of breast cancer 15%, recent research suggests." The data come from an observational study; therefore,

A West Coast university statistics professor wishes to determine which surfboard brand delivers consistently longer rides, Channel Island or JS. He recruits two of his students who surf to assist in an experiment, and the student assigned to the Channel Island board is determined by coin flip. The three head out to the beach for an afternoon, with the professor holding up a sign at random times for the respective student to catch the next wave on his board, and the time spent on that wave is recorded. This is repeated until each student has ridden 10 waves. The brand of surfboard in this story is:

A study compares the effect on college students of two different TV advertisements for spring break in Gulf Shores, Alabama. Call the ads "Ad #1" and "Ad #2." We want to know which ad makes more students want to visit Gulf Shores during spring break. The subjects are 90 students taking a course in hotel management. The design of the study looks like this: The response variable should be named in the outline at "Question C." The response variable in this study is

Does taking vitamins prevent colon cancer? A study assigned 864 subjects at random to four groups. One group took beta-carotene, another took vitamins C and E, a third took all three, and the fourth group took only a dummy pill. After four years, there was no difference among the groups in the formation of polyps in the colon that precede cancer. Does the new study (properly designed) give good reason to think that vitamins prevent colon cancer?

A study compares the effect on college students of two different TV advertisements for spring break in Gulf Shores, Alabama. Call the ads "Ad #1" and "Ad #2." We want to know which ad makes more students want to visit Gulf Shores during spring break. The subjects are 90 students taking a course in hotel management. The design of the study looks like this: The method used to form the groups appears in the diagram above at the point marked "Question A." This method is