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Chapter 1: Problem 9

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. In a study of whether taking a garlic supplement reduces the risk of getting a cold, 146 participants were assigned to either a garlic supplement group or to a group that did not take a garlic supplement (鈥淕arlic for the Common Cold," Cochrane Database of Systematic Reviews, 2009). Based on the study, it was concluded that the proportion of people taking a garlic supplement who get a cold is lower than the proportion of those not taking a garlic supplement who get a cold.

Short Answer

Expert verified
The given statistical study is an experiment because participants were assigned to different groups with varying conditions (garlic supplement intake). The researchers controlled which group received the garlic supplement and then compared the results for the two groups to draw a conclusion.

Step by step solution

01

The study's purpose is to examine whether taking a garlic supplement reduces the risk of getting a cold. The two variables involved are: 1. Garlic supplement intake (independent variable) 2. Risk of getting a cold (dependent variable) #tag_end# #Step 2: Determining if factors were manipulated#

The study involves assigning 146 participants to either a garlic supplement group or a group that did not take garlic supplements, which means one group received the supplement, and the other did not. The garlic supplement intake is being manipulated between the two groups. #tag_end# #Step 3: Classifying the study#
02

Since the garlic supplement intake is manipulated in this study, it is considered an experiment. An observational study would only involve gathering data from the participants without altering any factors. #tag_end# #Step 4: Justification for the classification#

The study is classified as an experiment because participants were assigned to different groups with varying conditions (garlic supplement intake). The researchers controlled which group received the garlic supplement and then compared the results for the two groups to draw a conclusion. #tag_end# So, the given statistical study is an experiment.

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Key Concepts

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

Observational Study
When we talk about statistical studies, an observational study is one where researchers observe subjects in a natural setting without any manipulation. They simply collect data based on what is already happening.

For instance, if we were looking at the relationship between diet and health, in an observational study, we would not change what participants eat; we would observe and record their eating habits and health outcomes over time. This can help identify correlations, but it can't establish causation because researchers do not control for variables; they observe them as is.
Experiment
Conversely, an experiment is a type of study where the researchers actively manipulate one variable to observe the effect on another. Importantly, experiments allow scientists to establish cause-and-effect relationships.

Going back to our dietary study, an experiment might involve giving some participants a specific diet to follow while others continue with their normal eating habits. By controlling one variable 鈥� in this case, diet 鈥� researchers can more definitively say whether it causes changes in health outcomes. The garlic supplement study, as detailed in the example given, is an experiment because the intake of the garlic supplement is purposely altered by the researchers.
Independent Variable
An independent variable is the one that researchers manipulate in an experiment. It's 'independent' because it doesn't change due to other variables; rather, it is the cause that researchers are testing.

Identifying the Independent Variable

In the garlic study, the independent variable is the intake of the garlic supplement. By assigning one group to take the garlic supplement and one group to not, the researchers are able to see if this variable independently affects the chances of getting a cold.
Dependent Variable
The dependent variable, on the other hand, is what researchers are trying to measure the effect on -- it 'depends' on the independent variable. After manipulation of the independent variable, researchers observe if there is a change in the dependent variable.

Measuring the Dependent Variable

In our example, the dependent variable is the risk of getting a cold. This is what the experiment aims to assess in relation to the intake of garlic supplements. If changes are observed in the risk of getting a cold based on whether or not the garlic supplement was taken, then researchers may conclude there is a cause-and-effect relationship.

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Most popular questions from this chapter

1.33 A study of college students showed a temporary gain of up to nine IQ points after listening to a Mozart piano sonata. This result, dubbed the Mozart effect, has since been criticized by a number of researchers who have been unable to confirm the result in similar studies. Suppose that you want to determine if there is really is a Mozart effect. You decide to carry out an experiment with three experimental groups. One group will listen to a Mozart piano sonata that lasts 24 minutes. The second group will listen to popular music for the same length of time, and the third group will relax for 24 minutes with no music playing. You will measure IQ before and after the 24 minute period. Suppose that you have 45 volunteers who have agreed to participate in the experiment. Describe the steps in a process you could use to randomly assign each of the volunteers to one of the experimental groups.

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 news release from Intel titled "Intel's Security International Internet of Things Smart Home Survey Shows Many Respondents Sharing Personal Data for Money" (March 30, 2016, newsroom.intel.com /news-releases/intel-securitys- international-internet-of -things-smart-home-survey/, retrieved September \(25,\) 2016) described a survey conducted in 2015 . The news release states "A total of 9,000 consumers were interviewed globally, including 2,500 from the United States, 1,000 from the United Kingdom, 1,000 from France, 1,000 from Germany, 1,000 from Brazil, 1,000 from India, 500 from Canada, 500 from Mexico and 500 from Australia." Among the findings from the survey were that \(54 \%\) of the respondents worldwide would be willing to share personal data collected from devices in their homes with companies in exchange for money.

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?

Use the following information to answer. The paper "Turning to Learn: Screen Orientation and Reasoning from Small Devices" (Computers in Human Behavior [2011]\(: 793-797)\) describes a study that investigated whether cell phones with small screens are useful for gathering information. The researchers wondered if the ability to reason using information read on a small screen was affected by the screen orientation. The researchers assigned 33 undergraduate students who were enrolled in a psychology course at a large public university to one of two groups at random. One group read material that was displayed on a small screen in portrait orientation, and the other group read material on the same size screen but turned to display the information in landscape orientation (see the following figure). The researchers found that performance on a reasoning test based on the displayed material was better for the group that read material in the landscape orientation. Is the study described above an observational study or an experiment?

The paper "Effect of a Nutritional Supplement on Hair Loss in Women" (Journal of Cosmetic Dermatology \([2015]: 76-82)\) describes an experiment to see if a dietary supplement consisting of Omega \(3,\) Omega \(6,\) and antioxidants could reduce hair loss in women with stage 1 hair loss. One hundred twenty women volunteered to participate in the study and were randomly assigned to either the supplement group or a control group. The women in the supplement group took the supplement for 6 months. Photos of the top of the head were taken of all the women at the beginning of the study and 6 months later at the end of the study. The two photos of each woman were evaluated by an independent expert who visually determined the change in hair density. The expert who determined the change in hair density did not know which of the women had taken the supplement. Answer the following seven questions for the described experiment. (Hint: Reviewing Examples 1.6 and 1.7 might be helpful.) 1\. What question is the experiment trying to answer? 2\. What are the experimental conditions (treatments) for this experiment? 3\. What is the response variable? 4\. What are the experimental units and how were they selected? 5\. Does the design incorporate random assignment of experimental units to the different experimental conditions? If not, are there potentially confounding variables that would make it difficult to draw conclusions based on data from the experiment? 6\. Does the experiment incorporate a control group and/ or a placebo group? If not, would the experiment be improved by including one or both of these? 7\. Does the experiment involve blinding? If not, would the experiment be improved by making it single- or double-blind?
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