Exam 5: Experiments, Good and Bad

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. In this study, the response variable 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. An example of a lurking variable that might affect the results of 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. This study is a(n):

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. In this study, the response variable is

Do doctors in managed care plans give less charity care? Researchers chose 60 communities at random, then chose doctors at random in each community. In all, they interviewed 10,881 doctors. Overall, 77.3% of the doctors said they had given some care free or at reduced rates because of the patient's financial need in the month before the interview. Doctors who received at least 85% of their practice income from managed care plans were significantly less likely than other doctors to provide charity care. The phrase "significantly less likely" means that, when we compare the charity work of doctors with more than 85% of their practice in managed care with other doctors,

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 St. John's wort study doesn't show that St. John's wort is equivalent to a placebo. If the researchers still believe in the effectiveness of St. John's wort in treating depression, how might they change their study?

An experiment on the effect of vitamin A on cancer uses two randomly chosen groups of 200 men each, one given vitamin A and the other a placebo. An estimate from a similar experiment using two groups of 1000 men each would have

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 explanatory variable in this study is:

A recent issue of the New England Journal of Medicine reports a study of all 122,754 infants born over an 8.5-year period at Parkland Hospital in Dallas, leaving out multiple births and infants with birth defects. The researchers wanted to know if there is a specific birth weight below which infant death and illness increases sharply. The explanatory variable in the study is

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 board they're riding on is not the only factor affecting the length of time they ride each wave. It is likely that the two surfing students are not identical in surfing ability. Since the professor is only interested in determining which surfboard brand delivers longer rides, the study suffers from:

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. This study is a(n)

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. The explanatory variable in this study is:

Hearing loss is more common among premature infants than among full-term infants. This was thought to be an effect of premature birth. It has recently been suggested that hearing loss may be caused by the high noise level of the incubators in which the premature infants are placed. This is an example of

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. In this study, the explanatory variable 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. An example of a lurking variable that might affect the results of this study is:

The most important advantage of experiments over observational studies is

Which of the following are the three principles of experimental design?

The drug manufacturer Merck recently stopped testing a promising new drug to treat depression. It turned out that in a randomized, double-blind trial a dummy pill did almost as well as the new drug. The fact that many people respond to a dummy treatment is called

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. Why is this study an experiment? Because:

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. In this study, the explanatory variable is: