Chapter 11-13

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  • 1/10 Questions

    In an experiment, if two variables are confounded, which of the following statements is true?

    • One of the variables must be lurking variables.
    • The variables will have a correlation coefficient greater than 0.5.
    • There is a clear indication that a placebo effect is present in the experiment.
    • The investigator cannot separate the effect of the variables on a response variable.
    • None of these is true.
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About This Quiz

Explore key statistical concepts through targeted questions in this Chapter 11-13 quiz. Assess your understanding of experimental design, confounding variables, observational studies, and more. Enhance your statistical reasoning and analytical skills.

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  • 2. 

    In one study on the effect of niacin on cholesterol level, 100 subjects who acknowledged being long-time niacin takers had their cholesterol levels compared with those of 100 people who had never taken niacin.  In a second study, 50 subjects were randomly chosen to receive niacin and 50 were chosen to receive a placebo.

    • The first study was a controlled experiment, while the second was an observational study.

    • The first study was an observational study, while the second was a controlled experiment.

    • Both studies were controlled experiments.

    • Both studies were observational studies.

    • Each study was part controlled experiment and part observational study.

    Correct Answer
    A. The first study was an observational study, while the second was a controlled experiment.
    Explanation
    The first study, where the cholesterol levels of long-time niacin takers were compared to those who had never taken niacin, is an observational study because the researchers did not manipulate any variables or assign subjects to specific groups. They simply observed and compared the existing groups. The second study, where subjects were randomly chosen to receive either niacin or a placebo, is a controlled experiment because the researchers manipulated the variable (niacin or placebo) and randomly assigned subjects to the groups.

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  • 3. 

    Blocking is utilized to help

    • Organize the treatment and control groups.

    • Counteract the placebo effect.

    • Produce groups that are as similar as possible.

    • Replicate the experiment with more subjects.

    • Avoid the need for randomization.

    Correct Answer
    A. Produce groups that are as similar as possible.
    Explanation
    Blocking is utilized to produce groups that are as similar as possible. Blocking involves dividing participants into subgroups based on certain characteristics or variables that may influence the outcome of the experiment. By doing so, researchers can ensure that each subgroup is represented equally in both the treatment and control groups, making them more comparable. This helps to minimize the impact of confounding variables and increase the internal validity of the study. Blocking is particularly useful when there are known variables that could potentially affect the outcome, allowing researchers to control for these variables and improve the accuracy of the experiment.

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  • 4. 

    A personnel director at a large company studied the eating habits of employees by watching the movement of a selected group of employees at lunchtime.  The purpose of the study was to determine the proportion of employees who buy lunch in the cafeteria, bring their own lunches, or go out to lunch.  If the director were to include all of the employees in her study, she is performing a 

    • Simple random sample

    • Quota sample

    • Convenience sample

    • Multi-stage cluster sample

    • Census

    Correct Answer
    A. Census
    Explanation
    The personnel director is performing a census because she is studying the eating habits of all employees at the company, not just a selected group. A census involves collecting data from every member of a population, in this case, all employees. This allows for accurate and comprehensive information about the proportion of employees who buy lunch in the cafeteria, bring their own lunches, or go out to lunch.

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  • 5. 

    A study is made to determine whether studying Latin helps students achieve higher scores on the verbal section of the SAT exam.  In comparing records of 200 students, half of whom have taken at least 1 year of Latin, it is noted that the average SAT verbal score is higher for those 100 students who have taken Latin than for those who have not.  Based on this study, guidance counselors begin to recommend Latin for students who want to do well on the SAT exam.  Which of the following are true statements? I.  While this study indicates a relation, it does not prove causation. II.  There could well be a confounding variable responsible for the seeming relationship. III.  Self-selection here makes drawing the counselors' conclusion difficult.

    • I and II

    • I and III

    • II and III

    • I, II and III

    • None of the above gives the complete set of true responses.

    Correct Answer
    A. I, II and III
    Explanation
    The study shows a correlation between studying Latin and higher SAT verbal scores, but it does not prove that studying Latin causes higher scores. There could be other factors (confounding variables) that contribute to the relationship observed. Additionally, the study is limited by self-selection, as students who choose to take Latin may already have certain characteristics that make them more likely to achieve higher scores on the SAT. Therefore, all three statements are true.

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  • 6. 

    A nutritionist believes that having each player take a vitamin pill before a game enhances the performance of the football team.  During the course of one season, each player takes a vitamin pill before each game, and the team achieves a winning season for the first time in several years.  Is this an experiment or an observational study?

    • An experiment, but with no reasonable conclusion possible about cause and effect.

    • An experiment, thus making cause and effect a reasonable conclusion.

    • An observational study, because there was no use of a control group.

    • An observational study, but a poorly designed one because randomization was not used.

    • An observational study, thus allowing a reasonable conclusion of association but not of cause and effect.

    Correct Answer
    A. An experiment, but with no reasonable conclusion possible about cause and effect.
    Explanation
    This is an experiment because the nutritionist intentionally instructs the players to take a vitamin pill before each game. However, no reasonable conclusion can be made about cause and effect because there is no control group or randomization. Without a control group, it is difficult to determine if the improved performance is solely due to the vitamin pill or other factors. Therefore, while it is an experiment, it does not provide enough evidence to establish a causal relationship between taking the vitamin pill and the team's winning season.

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  • 7. 

    Which of the following situations qualifies as an observational study?

    • The girls at your high school are surveyed to determine if they believe there is any sexual stereotyping in the school newspaper.

    • Two flowerpots are planted with the same type of seed. One is given 0.2 cups of water each day while the other is given 0.5 cups of water each day. At the end of one month, the growth of each plant is observed and measured.

    • A student flips a coin 100 times and records the number of heads.

    • None of these are observational studies.

    Correct Answer
    A. The girls at your high school are surveyed to determine if they believe there is any sexual stereotyping in the school newspaper.
    Explanation
    The correct answer is the first option, "The girls at your high school are surveyed to determine if they believe there is any sexual stereotyping in the school newspaper." This qualifies as an observational study because it involves observing and collecting data without any intervention or manipulation of variables. The researchers are simply surveying the girls to gather their opinions and beliefs about sexual stereotyping in the school newspaper.

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  • 8. 

    Each of the 29 NBA teams has 12 players.  A sample of 58 players is to be chosen as follows.  Each team will be asked to place 12 cards with their players names into a hat and randomly draw out two names.  The two names from each team will be combined to make up the sample.  Will this method result in a simple random sample of the 348 basketball players?

    • Yes, because each player has the same chance of being selected.

    • Yes, because each team is equally represented.

    • Yes, because this is an example of stratified sampling, which is a special case of simple random sampling.

    • No, because the teams are not chosen randomly.

    • No, because not each group of 58 players has the same chance of being selected.

    Correct Answer
    A. No, because not each group of 58 players has the same chance of being selected.
    Explanation
    The given method will not result in a simple random sample of the 348 basketball players because not each group of 58 players has the same chance of being selected. In this method, the players are selected based on their team affiliation, rather than being chosen randomly from the entire pool of players. This means that some players may have a higher probability of being selected if their team has a larger representation in the sample. Therefore, the method does not meet the criteria of simple random sampling.

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  • 9. 

    The student council of your high school wants to conduct a survey regarding the dress code for school dances.  You have advised them that it might be best to conduct a stratified random sample of the student body.  Which of the following is not a valid stratified design?  Assume the results of the separate samples will be combined into a single sample of the student body.

    • Two simple random samples are to be conducted: one of the boys in the student body and the other of the girls in the student body.

    • Four simple random samples are conducted: one in each of the four classes.

    • Two simple random samples are conducted in randomly selected homerooms: one of the boys in the selected homerooms and the other of the girls in the selected homerooms.

    • Two random samples are conducted: one of students whose GPA's are 2.5 or higher and the other of students whose GPA's are less than 2.5.

    • None of these statements is a valid design.

    Correct Answer
    A. Two simple random samples are conducted in randomly selected homerooms: one of the boys in the selected homerooms and the other of the girls in the selected homerooms.
    Explanation
    This design is not a valid stratified design because it does not divide the population into mutually exclusive and exhaustive groups. In this design, the boys and girls are selected separately, but there is no guarantee that every student will be included in one of these groups. A valid stratified design would ensure that every student is assigned to either the boys or girls group, and then random samples would be taken from each group.

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  • 10. 

    A simple random sample was selected of large urban school districts throughout New England.  The selected districts were identified as target districts.  Within each district, a simple random sample of its high schools was chosen and the principals of those high schools were interviewed.  Which of the following statements regarding this design is NOT true?

    • The is an example of a multi-stage cluster sample.

    • Results from the interviews cannot be used to infer responses of the population of interest.

    • The population of interest is the set of all high school principals in New England.

    • Not every subset of principals has the same chance of selection.

    • All of these statements are true.

    Correct Answer
    A. Results from the interviews cannot be used to infer responses of the population of interest.
    Explanation
    This design is an example of a multi-stage cluster sample, as it involves selecting school districts as the first stage and then selecting high schools within each district as the second stage. The population of interest is the set of all high school principals in New England, as the design aims to gather information from these individuals. Not every subset of principals has the same chance of selection, as the design involves simple random sampling at both the district and high school levels. However, results from the interviews can be used to infer responses of the population of interest, as the design aims to gather information from high school principals in New England.

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  • Mar 20, 2023
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    Dimsdale
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