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For each of the statistical studies described, indicate whether the study is an observational study or an experiment. Give a brief explanation for your choice. A paper appearing in The Journal of Pain (March 2010 , 199-209) described a study to determine if meditation has an effect on sensitivity to pain. Study participants were assigned to one of three groups. One group meditated for 20 minutes; one group performed a distraction task (working math problems!) for 20 minutes; and one group practiced a relaxation technique for 20 minutes. Sensitivity to pain was measured both before and after the 20 -minute session.

The article "Bicyclists and Other Cyclists" (Annals of Emergency Medicine [2010]: 426) reported that in 2008 , 716 bicyclists were killed on public roadways in the United States and that the average age of the cyclists killed was 41 years. These figures were based on an analysis of the records of all traffic-related deaths of bicyclists on U.S. public roadways (this information is kept by the National Highway Traffic Safety Administration). a. Does the group of 716 bicycle fatalities represent a census or a sample of the bicycle fatalities in 2008 ? b. If the population of interest is bicycle traffic fatalities in 2008 , is the given average age of 41 years a statistic or a population characteristic?

"Should You Get a Flu Shot? Your Physical and Financial Health Is on the Line" is the title of an article that appears in a blog on the WalletHub web site (December 20 , 2013, wallethub.com/blog/flu-shot-survey/1303/, retrieved September 25,2016 ). The author reported that an infectious disease expert from a top medical school in each of the 50 states was asked if he or she would recommend that the average person get a flu shot. Based on the 50 responses, it was reported that \(94 \%\) would recommend a flu shot. a. Suppose that the purpose of this survey was to estimate the percentage of all doctors who would recommend a flu shot. Would this sample be a simple random sample, a stratified sample, a systematic sample, or a convenience sample? Explain. b. Explain why an estimate of the percentage who would recommend a flu shot that was based on data from this sample should not be generalized to all doctors.

A survey of Arizona drivers is described in the article "Study Claims Safety Should Be Made Law" (Red Rock News, August 21,2015\()\). The following statement is from the article: According to the annual survey, which aims to gauge the opinions and concerns of the motoring public across the state regarding traffic safety, Arizona drivers want better traffic safety laws. The survey showed that nine in 10 Arizonans -91 percent \(-\) favor a statewide ban on texting while driving for all drivers, and about two-thirds -64 percent \(-\) favor a primary seat belt law. The article also describes how the data for this survey were collected. A survey was mailed to 2500 randomly selected AAA Arizona members (AAA Arizona is an automobile club that provides services to approximately 860,000 members in Arizona). The article did not indicate how many of the surveys were actually returned. The results of this survey were generalized to all Arizona drivers. Answer the following four questions for this observational study. (Hint: Reviewing Examples 1.4 and 1.5 might be helpful.) a. What is the population of interest? b. Was the sample selected in a reasonable way? c. Is the sample likely to be representative of the population of interest? d. Are there any obvious sources of bias?

The supervisors of a rural county are interested in the proportion of property owners who support the construction of a sewer system. Because it is too costly to contact all 7000 property owners, a survey of 500 owners (selected at random) is undertaken. Describe the population and the sample for this problem.

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.

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.

In an experiment to compare two different surgical procedures for hernia repair ("A Single-Blinded, Randomized Comparison of Laparoscopic Versus Open Hernia Repair in Children," Pediatrics [2009]: 332-336), 89 children were assigned at random to one of the two surgical methods. The methods studied were laparoscopic repair and open repair. In laparoscopic repair, three small incisions are made, and the surgeon works through these incisions with the aid of a small camera that is inserted through one of the incisions. In the open repair, a larger incision is used to open the abdomen. One of the response variables was the amount of medication given after the surgery to control pain and nausea. The paper states, "For postoperative pain, rescue fentanyl ( \(1 \mathrm{mg} / \mathrm{kg}\) ) and for nausea, ondansetron \((0.1 \mathrm{mg} / \mathrm{kg})\) were given as judged necessary by the attending nurse blinded to the operative approach." a. Why do you think it was important that the nurse who administered the medications did not know which type of surgery was performed? b. Explain why it was not possible for this experiment to be double-blind.

Use the following information to answer Exercise. Many surgeons play music in the operating room. Does the type of music played have an effect on the surgeons' performance? The report "Death Metal in the Operating Room" (NPR, December 24, 2009, www.npr.org, retrieved April 8,2017 ) describes an experiment in which surgeons used a simulator to perform a surgery. Some of the surgeons listened to music with vocal elements while performing the surgery, and others listened to music that did not have vocal elements. The researchers concluded that the average time to complete the surgery was greater when music with vocal elements is played than when music without vocal elements is played. Explain why it is important that the surgeons be assigned at random to the two music conditions in the experiment described above.

A study described in Food Network Magazine (January 2012) concluded that people who push a shopping cart at a grocery store are less likely to purchase junk food than those who use a hand-held basket. a. Do you think this study was an observational study or an experiment? b. Is it reasonable to conclude that pushing a shopping cart causes people to be less likely to purchase junk food? Explain why or why not.