ST 351 - Lesson 4 Practice Problems
31 a-c) Hamstrings: Exercise 19 discussed an experiment to see if the time it took athletes with hamstring injuries to be able to return to sports was different depending on which of two exercise programs they engaged in. a) Explain why it was important to assign the athletes to the two different treatments randomly b) There was no control group consisting of athletes who did not participate in a special exercise program. Explain the advantage of including such a group. c) How might blinding have been used?
a) Allowing the athletes to choose their own treatments could confound the results. Other issues such as severity of the injury, diet, age, etc could also affect time to heal, and randomization should equalize the two treatment groups with respect to any such variables. b) A control group could have revealed whether either exercise program was better/worse than just letting the injury heal without exercise. c) Although the athletes cannot be blinded, the doctors who approve their return to sports should not know which treatment the subject had engaged in.
29) Shoes: A running-shoe manufacturer wants to test he effect of it new sprinting shoe on 100-meter dash times. The company sponsors 5 athletes who are running the 100-meter dash in 2004 Summer Olympic games. To test the shoe, it has all 5 runners run the 100-meter dash with a competitor's shoe and then again with their new shoe. The company uses the difference in times as the response variable. a) Suggest some improvements to the design b) Why might the shoe manufacturer not be able to generalize the results they find to all runners?
a) First, the manufacturers are using athletes who have a vested interest in the success of the shoe by virtue of their sponsorship. They should try to find some volunteers that aren't employed by the company. Second, they should randomize the order of the runs, not run all the races with new shoe second. They should blind the athletes by disguising the shoes, if possible, so they don't know which is which. The experiment could be double-blinded, as well, by making sure the timers don't know which shoe is being tested at any given time. Finally, they should replicate the experiment several times since times will vary under both shoe conditions. b) First of all, the problems identified in part a) would have to be addressed before any conclusions can be reached. Even if this is the case, the results cannot be generalized to all runners. This experiment compares the effects of the shoes on the speed for Olympic class runners, not runners in general.
35) Wine: A 2001 Danish study published in the Archives of Internal Medicine casts significant doubt on suggestions that adults who drink wine have higher levels of "good" cholesterol and fewer heart attacks. These researchers followed a group of individuals born at a Copenhagen hospital between 1959 and 1961 for 40 years. Their study found that in this group the adults who drank more wine were richer and better educated that those who did not. a) What kind of study was this? b) It is generally true that people with high levels of education and high socioeconomic status are healthier than others. How does this call into question the supposed health benefits of wine? c) Can studies such as these prove causation (that wine helps prevent heart attacks, that drinking wine makes one richer, that being rich helps prevent heart attacks, etc)? Explain.
a) This is a prospective observational study. The researchers followed a group of children born at a Copenhagen hospital between 1959-1961. b) The results of the Danish study report a link between high socioeconomic status, education, and wine drinking. Since people with high levels of education and higher socioeconomic status are also more likely to be healthy, the relationship between health and wine consumption might be explained by the confounding variables of socioeconomic status and education. c) Studies such as these prove none of these. While the variables have a relationship there are no indications of a cause-and-effect- relationship. The only way to determine causation is through a controlled, randomized, and replicated experiment.
3) MS and Vitamin D: Multiple sclerosis (MS) is an autoimmune disease that strikes more often the farther people live from the equator. Could vitamin D - which most people get from the sun's ultraviolet rays - be a factor? Researchers compared vitamin D levels in blood samples from 150 US military personnel who have developed MS with blood samples of nearly 300 who have not. The samples were taken, on average, five years before the disease was diagnosed. Those with the highest blood vitamin D levels had a 62% lower risk of MS than those with the lowest levels. (The link was only in whites, not in blacks or Hispanics). a) What kind of study was this? b) Is that an appropriate choice for investigating this problem? Explain. c) Who were the subjects? d) What were the variables?
a) This is a retrospective observational study b) It is an appropriate choice for investigating this problem because MS is a relatively rare disease c) The subjects were the US military personnel, some who had developed MS d) The variables were the Vitamin D blood levels and whether or not the subject developed MS
19) Athletes who had suffered hamstring injuries were randomly assigned to one of two exercise programs. Those who engaged in static stretching returned to sports activity in a mean of 15.2 days faster than those assigned to a program of agility and trunk stabilization exercises.
a) This is an experiment. Athletes were randomly assigned to one of two exercise programs b) The subjects are athletes suffering from hamstring injuries c) There is one factor (type of exercise), at 2 levels (static stretching versus agility and trunk stabilization) d) 1 factor, at 2 levels, results in 2 treatments e) The response variable is the time before the athletes were able to return to sports f) The experiment was completely randomized g) The experiment employs no blinding. The subjects know what kind of exercises they do. h) Assuming that the athletes actually follow the exercise program, this experiment can help determine which of the two exercise programs is more effective at rehabilitating hamstring injuries.
17) Some people claim they can get relief from migraine headache pain by drinking a large glass of ice water. Researchers plan to enlist several people who suffer from migraines in a test. When a participant experiences a migraine headache, s/he will take a pill that may be a standard pain reliever or a placebo. Half of each group will also drink ice water. Participants will then report the level of pain relief they experience.
a) This is an experiment. Subjects were randomly assigned to treatments b) The subjects were people experiencing migraines c) There were 2 factors (pain reliever and water temperature). The pain reliever factor has 2 levels, (pain reliever or placebo), and the water temperature factor has 2 levels (ice water and regular water) d) 2 factors at 2 levels each, results in 4 treatments e) The response variable is the level of pain relief f) The experiment is completely randomized g) The subjects are blinded to the pain reliever factor through the use of placebo. The subjects were not blinded to the water factor. They will know whether they are drinking ice water or regular water. h) The experiment may indicate whether pain reliever alone or in combination with ice water give pain relief, but patients are not blinded to the ice water, so the placebo effect may also be the cause of any relief seen due to ice water.
5) Menopause: Researchers studied the herb black cohosh as a treatment for hot flashes caused by menopause. They randomly assigned 351 women aged 45-55 who reported at least 2 hot flashes a day to one of five groups: 1) black cohosh, 2) a multiherb supplement with black cohosh, 3) the multiherb supplement plus advice to consume more soy products, 4) estrogen replacement therapy, or 5) placebo. After a year, only the women given estrogen replacement therapy had symptoms different than those of the placebo group. a) What kind of study was this? b) Is that an appropriate choice for this problem? c) Who were the subjects? d) Identify the treatment and response variables
a) This was a randomized, comparative, placebo-controlled experiment b) Yes, such an experiment is the right way to determine whether black cohosh is an effective treatment for hot flashes c) The subjects were 351 women, between the ages of 45-55, who reported at least 2 hot flashes a day d) The treatments were black cohosh, a multiherb supplement, plus advice to consume more soy products, estrogen, and a placebo. The response was the women's self-reported symptoms, presumably the frequency of hot flashes.
13) In 2002, the journal Science reported that a study of women in Finland indicated that having sons shortened the lifespans of mothers by about 34 weeks per son, but that daughters helped lengthened the mother's lives. The data came from church records from the period 1640 to 1870.
a) This was an observational study b) The study is retrospective since the results were obtained from pre-existing church records c) The subjects of the study are women in Finland. The data were collected from church records dating from 1640-1870, but the selection process is unknown. d) The parameter of interest is the difference in the average lifespan between mothers of sons and daughters e) For this group, having sons was associated with a decrease in lifespan of an average of 34 weeks per son, while having daughters was associated with an unspecified increase in lifespan. As there, is no random assignment, there is no way to know that having sons caused a decrease in lifespan
15) The May 4, 2000 issue of Science News reported that, contrary to popular belief, depressed individuals cry no more often in response to sad situations than non-depressed people. Researchers studied 23 men and 48 women with major depression and 9 men and 24 women with no depression. They showed the subjects a sad film about a boy whose father has died, noting whether or not the subjects cried. Women cried more often than men, but there were no significant differences between the depressed and non-depressed groups.
a) This was an observational study (although some may say that the sad movie was "imposed" on the subjects, it was merely a stimulus used to trigger a reaction, not a treatment designed to attempt to influence some response variable. Researchers merely wanted to observe the behavior of two different groups when each was presented with the stimulus) b) The study was prospective. The researchers identified the subjects, and then observed them after the movie c) The subjects were people with and without depression. The selection process was never stated. d) The parameter of interest is the difference in crying response between depressed/non-depressed people that were exposed to sad situations e) There is no apparent difference in crying response to sad movies for the depressed/non-depressed people