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Chapter 1: Problem 31

1.31 In an experiment to assess the effect of wearing compression socks during a marathon, 20 runners in the 2013 Hartford Marathon were randomly assigned to two groups ("Compression and Clots in Athletes Who Travel," Lower Extremities Review, lermagazine.com/ler-archives/january -2016, retrieved July 2, 2017). Runners in one group wore a pair of compression socks during the marathon, while runners in the second group wore regular athletic socks. At the end of the marathon, blood samples were taken to measure variables related to preventing blood clots and speeding up recovery from exercise. a. Describe why it was important for the researchers to assign participants to one of the two groups rather than letting the participants choose which group they wanted to be in. b. The authors of the paper state that there is some evidence that suggests that wearing compression socks may result in a psychological advantage that might translate into performance gains. Suppose that instead of a response variable that was determined by a blood test, the response variable had been the time it took the runner to complete the marathon. Do you think it would be a good idea to have the runners be blind to the type of socks that they were given? Explain why or why not.

Short Answer

Expert verified
In summary, random assignment is essential in experimental designs to eliminate potential confounding variables and ensure a fair comparison between the groups. Keeping runners blind to the type of socks they are wearing, especially if the response variable is the marathon completion time, eliminates any potential psychological advantages or biases and provides a more accurate understanding of the true effect of the socks on performance.

Step by step solution

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a. Importance of random assignment

Assigning participants to the groups randomly is important in experimental designs to create two groups that are as similar as possible, eliminating potential confounding variables and allowing for a fair comparison between the groups. This ensures that any differences observed between the groups can be attributed to the treatment being tested (in this case, wearing compression socks) and not to other factors. When participants self-select or when they are not randomly assigned, there is a higher chance of selection bias, where the two groups might be inherently different, which could affect the validity of the conclusions drawn from the experiment.
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b. Runners being blind to the type of socks

If the response variable was the time it took the runner to complete the marathon, it would be a good idea to keep the runners blind to the type of socks they are wearing because it would eliminate any potential psychological advantage that might influence their performance. If the runners knew which type of socks they are wearing, their performance may be affected by their beliefs about the benefits of compression socks, which can ultimately lead to bias in the results. By making the runners blind to the type of socks, the experiment would provide a more accurate understanding of the true effect of the socks on the marathon completion time.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Random Assignment
When conducting research in the field of statistics, the use of random assignment is a critical step in experimental design. This process involves randomly allocating participants into different groups to ensure that each participant has an equal chance of being placed in any given condition. By doing so, researchers minimize the risk of confounding variables, which are external influences that could skew the study鈥檚 results. In the study regarding compression socks during a marathon, random assignment prevents the possibility of participants with a prior preference for compression socks, perhaps due to past experiences, from all ending up in one group. This randomization helps simulate a natural distribution of various participant characteristics across both the compression sock and regular athletic sock groups. Therefore, it allows for a fair and unbiased comparison, assuming the only difference between the groups is the treatment鈥攃ompression socks in this case.
Control Groups
A control group in an experiment serves as a baseline to compare against the experimental or treatment group. It is essential to have a control group to understand the effect of the variable being tested. In our experiment concerning marathon runners, the control group is the one wearing regular athletic socks. These runners provide a comparison for evaluating the impact of wearing compression socks. Without this group, there would be no way to determine if compression socks truly have an effect, or if any observed changes were due to other external factors like weather, training level, or individual health conditions.
Blinding in Experiments
In a well-designed experiment, blinding is used to eliminate bias. The concept involves keeping participants, and sometimes the researchers, unaware of which group they are in with respect to receiving the treatment or control condition. If we consider the proposed scenario where the marathon time was the response variable, blinding the runners to their sock type is beneficial. This approach removes any psychological effect, such as a placebo or performance anxiety, that knowledge of their group assignment might induce. For the experiment with compression socks, not knowing which type of sock they are wearing helps ensure that any observed differences in performance are likely due to the physical benefits of the socks, rather than runners' psychological state.
Confounding Variables
In experimental research, confounding variables can greatly interfere with the interpretation of results. These are variables that the researcher failed to control or eliminate, which can lead to a false association between the treatment and the observed effect. Suppose a prominent runner known for record-setting times swears by compression socks, influencing other participants who may believe in their efficacy. This scenario shows a potential confounder: the runners' beliefs about compression socks. By randomly assigning runners to either compression or regular socks and ensuring they are blind to their sock type, the study reduces the impact of this confounding variable, thereby providing clearer insight into the true effects of compression socks on performance and recovery.

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Most popular questions from this chapter

The article "How Dangerous Is a Day in the Hospital?" (Medical Care [2011]: 1068-1075) describes a study to determine if the risk of an infection is related to the length of a hospital stay. The researchers looked at a large number of hospitalized patients and compared the proportions who got an infection for two groups of patients-those who were hospitalized overnight and those who were hospitalized for more than one night. Indicate whether the study is an observational study or an experiment. Give a brief explanation for your choice.

For each of the following, determine whether the statistical study described is an observational study or an experiment. Give a brief explanation of your choice. a. Can choosing the right music make wine taste better? This question was investigated by a researcher at a university in Edinburgh (www.decanter.com/wine-news /montes-music-makes-wine-reach-parts-it-otherwise -couldnt-reach-82325/, retrieved April 8,2017 ). Each of 250 volunteers was assigned at random to one of five rooms where they were asked to taste and rate a glass of wine. No music was playing in one of the rooms, and a different style of music was playing in each of the other four rooms. The researcher concludedFor each of the following, determine whether the statistical study described is an observational study or an experiment. Give a brief explanation of your choice. a. Can choosing the right music make wine taste better? This question was investigated by a researcher at a university in Edinburgh (www.decanter.com/wine-news /montes-music-makes-wine-reach-parts-it-otherwise -couldnt-reach-82325/, retrieved April 8,2017 ). Each of 250 volunteers was assigned at random to one of five rooms where they were asked to taste and rate a glass of wine. No music was playing in one of the rooms, and a different style of music was playing in each of the other four rooms. The researcher concluded that cabernet sauvignon is rated more highly when bold music is played than when no music is played. b. The article "Display of Health Risk Behaviors on MySpace by Adolescents" (Archives of Pediatrics and Adolescent Medicine [2009]: 27-34) described a study of 500 publically accessible MySpace web profiles posted by 18 -year- olds. The content of each profile was analyzed and the researchers concluded that those who indicated involvement in sports or a hobby were less likely to have references to risky behavior (such as sexual references or references to substance abuse or violence). c. USA TODAY (January 29,2003 ) reported that in a study of affluent Americans (defined as those with incomes of \$ 75,000\( or more per year) \)57 \%$ indicated that they would rather have more time than more money. d. The article "Acupuncture for Bad Backs: Even Sham Therapy Works" (Time, May 12,2009 ) summarized a study conducted by researchers at the Group Health Center for Health Studies in Seattle. In this study, 638 adults with back pain were randomly assigned to one of four groups. People in group 1 received the usual care for back pain. People in group 2 received acupuncture at a set of points tailored specifically for each individual. People in group 3 received acupuncture at a standard set of points typically used in the treatment of back pain. Those in group 4 received fake acupuncture- they were poked with a toothpick at the same set of points used for the people in group 3 . Two notable conclusions from the study were: (1) patients receiving real or fake acupuncture experienced a greater reduction in pain than those receiving usual care; and (2) there was no significant difference in pain reduction between those who received real acupuncture (groups 2 and 3 ) and those who received fake acupuncture toothpick pokes.

The article "Doctor Dogs Diagnose Cancer by Sniffing It Out" (Knight Ridder Newspapers, January 9, 2006) refers to an experiment described in the journal Integrative Cancer Therapies. In this experiment, dogs were trained to distinguish between people with breast and lung cancer and people without cancer by sniffing exhaled breath. Dogs were trained to lie down if they detected cancer in a breath sample. After training, the dogs' ability to detect cancer was tested using breath samples from people whose breath had not been used in training the dogs. The paper states, "The researchers blinded both the dog handlers and the experimental observers to the identity of the breath samples." Explain why this blinding is an important aspect of the design of this experiment.

Does playing action video games provide more than just entertainment? The authors of the paper "Action-VideoGame Experience Alters the Spatial Resolution of Vision" (Psychological Science [2007]: 88-94) concluded that spatial resolution, an important aspect of vision, is improved by playing action video games. They based this conclusion on data from an experiment in which 32 volunteers who had not played action video games were "equally and randomly divided between the experimental and control groups." Subjects in each group played a video game for 30 hours over a period of 6 weeks. Those in the experimental group played Unreal Tournament 2004 , an action video game. Those in the control group played Tetris, a game that does not require the user to process multiple objects at once. Explain why it was important for the researchers to randomly assign the subjects to the two groups.

"Pecans Lower Cholesterol" is a headline that appeared in the magazine Woman's World (November 1 , 2010). Consider the following five study descriptions. For each of the study descriptions, answer these five questions: Question 1: Is the described study an observational study or an experiment? Question 2: Did the study use random selection from some population? Question 3: Did the study use random assignment to experimental groups? Question 4: Would the conclusion "pecans lower cholesterol" be appropriate given the study description? Explain. Question 5: Would it be reasonable to generalize conclusions from this study to some larger population? If so, what population? Study 1: Five hundred students were selected at random from those enrolled at a large college in Florida. Each student in the sample was asked whether they ate pecans more than once in a typical week, and their cholesterol levels were also measured. The average cholesterol level was significantly lower for the group who ate pecans more than once a week than for the group that did not. Study 2: One hundred people who live in Los Angeles volunteered to participate in a statistical study. The volunteers were divided based on gender, with women in group 1 and men in group \(2 .\) Those in group 1 were asked to eat 3 ounces of pecans daily for 1 month. Those in group 2 were asked not to eat pecans for 1 month. At the end of the month, the average cholesterol level was significantly lower for group 1 than for group 2 Study 3: Two hundred people volunteered to participate in a statistical study. Each person was asked how often he or she ate pecans, and their cholesterol levels were also measured. The average cholesterol level for those who ate pecans more than once a week was significantly lower than the average cholesterol level for those who did not eat pecans. Study 4: Two hundred people volunteered to participate in a statistical study. For each volunteer, a coin was tossed. If the coin landed heads up, the volunteer was assigned to group 1 . If the coin landed tails up, the volunteer was assigned to group 2 . Those in group 1 were asked to eat 3 ounces of pecans daily for 1 month. Those in group 2 were asked not to eat pecans for 1 month. At the end of the month, the average cholesterol level was significantly lower for group 1 than for group 2 . Study 5: One hundred students were selected at random from those enrolled at a large college. Each of the selected students was asked to participate in a study, and all agreed to participate. For each student, a coin was tossed. If the coin landed heads up, the student was assigned to group 1 . If the coin landed tails up, the student was assigned to group \(2 .\) Those in group 1 were asked to eat 3 ounces of pecans daily for 1 month. Those in group 2 were asked not to eat pecans for 1 month. At the end of the month, the average cholesterol level was significantly lower for group 1 than for group 2 .
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