Deck 12: Experimental Design: Controlling Variation

Question 1

Use the following information for following questions:. Which treatment is most effective at
treating bathroom mildew: water mixed with vinegar, ammonia, or soap? In a study, researchers randomly
assigned 55 similar tile samples with similar amounts of mildew to one of three groups. Depending on
which group they were assigned to, each tile sample received a home remedy of water mixed with
vinegar, ammonia, or soap. Afterwards, each tile sample was examined and any remaining mildew was
measured. Researchers found that a soap and water mixture produced better results than both vinegar and
ammonia.
Write a statement that restates the conclusion of the study in terms of a cause-and-effect conclusion.

Answer 1

A soap and water mixture effectively treats mildew stains on tile compared to vinegar and ammonia.

Question 2

Use the following information for following questions:. A researcher wonders whether length of
time that it takes to hail a taxi is affected by the gender of the person hailing the taxi. The researcher used
the following study design to collect data: The researcher chose five busy intersections in a large city and
recorded the number of males and females who hailed a taxi. He also records how long it took to get a
taxi to stop. He finds that male customers waited a shorter period of time than females waited for a taxi.
Restate the conclusion of the study in terms of a cause-and-effect conclusion. Explain why we can or cannot make a cause-and-effect conclusion.

Answer 2

Possible cause-and-effect conclusion: Being male leads to shorter wait times for a taxi, a new study finds. This was an observational study. Since random assignment was not used, we cannot conclude that being male caused the taxis to stop faster.

Question 3

A study is to be undertaken to determine the teacher workload in the public schools in a large county in California. The target population is all high school teachers (grades 9 - 12) with at least one year of experience. The county contains a total of thirty-seven public high schools and a total of 4,857 teachers. All teachers selected in the sample will be asked to complete a short survey. Describe a sampling plan that would allow the researchers to obtain the desired information.

Answer 3

Answers will vary, but cluster sampling is likely to be a reasonable choice. One could randomly select high schools from the thirty-seven and then survey all teachers in the selected high schools.

Question 4

Does listening to music improve efficiency for mundane tasks? In a study, researchers randomly assigned 50 similar adults to one of three groups. All subjects were asked to stuff 400 envelopes. Depending on which group they were assigned to, subjects heard Top 40 music, classical music, or no music while they worked. Researchers recorded how long it took the participants to stuff the envelopes. Researchers found that the adults that listened to no music completed the work faster than both the group that listened to Top 40 music and classical music. For this controlled experiment, state the treatment and the response variables.

Question 5

Suppose the president of a large company is in the process of deciding whether to adopt a lunchtime exercise program.The purpose of the program is to improve the health of the employees and thus, reduce the medical expenses. To get more information, he instituted the exercise program for all the employees in one office. The president knows that during the winter months medical expenses are relatively high because of high occurrences of colds and flu. Therefore, he records the medical expenses of the employees in the

Question 6

Use the following information for following questions:. A researcher wonders whether length of
time that it takes to hail a taxi is affected by the gender of the person hailing the taxi. The researcher used
the following study design to collect data: The researcher chose five busy intersections in a large city and
recorded the number of males and females who hailed a taxi. He also records how long it took to get a
taxi to stop. He finds that male customers waited a shorter period of time than females waited for a taxi.
Explain why we can or cannot generalize these results to a larger population.

Question 7

Write at least two questions that you should ask yourself when reading articles containing statistical research results. Explain why these questions are important.

Question 8

selected office for each of the twelve months prior to the exercise program and then for each of the
twelve months after the exercise program is initiated. The "before" and "after" expenses are
compared on a month-to-month basis. Which test design would be the most appropriate for this
scenario?
Recently, it was reported that the proportion of people using seatbelts while driving has begun to drop after years of steady increases. To determine the proportion of drivers using seatbelts in a particular community, it was decided to set up a checkpoint on a busy road and stop every twentieth driver to see if he/she was using a seatbelt. What kind of sampling does this illustrate?

Question 9

selected office for each of the twelve months prior to the exercise program and then for each of the
twelve months after the exercise program is initiated. The "before" and "after" expenses are
compared on a month-to-month basis. Which test design would be the most appropriate for this
scenario?
A corporation desires to estimate the total number of worker-hours lost for a given month because of accidents among all employees. Because laborers, technicians, and administrators have different accident rates, the researcher decides to randomly select employees from each of the three groups and records the number of worker-hours lost for the given month for each employee. What kind of sampling does this illustrate?

Question 10

selected office for each of the twelve months prior to the exercise program and then for each of the
twelve months after the exercise program is initiated. The "before" and "after" expenses are
compared on a month-to-month basis. Which test design would be the most appropriate for this
scenario?
A researcher is interested in knowing how satisfied people who live in independent living facilities are with their living conditions. To answer this question, the researcher randomly selects 50 independent living facilities from throughout the United States and asks each resident of the selected facilities how satisfied he/she is with his/her current living conditions. What kind of sampling does this illustrate?

Question 11

Use the following information for following questions:. These two headlines are on the same topic.
Headline A: Children who view advertisements for fast food dramatically increase their risk of becoming
obese adolescents, a new study suggests.
Headline B: Viewing advertisements for fast food leads to childhood obesity, a new study finds.
Which one has language that suggests a cause- and effect relationship? Is this problematic? Can you think of a confounding factor other than exposure to fast food advertisements that might cause childhood obesity?

Question 12

selected office for each of the twelve months prior to the exercise program and then for each of the
twelve months after the exercise program is initiated. The "before" and "after" expenses are
compared on a month-to-month basis. Which test design would be the most appropriate for this
scenario?
Describe one benefit to a stratified sampling plan.

Question 13

Suppose it was reported on the news that a recent study concluded that pollutants in the air have dramatically increased our chances of getting a rare form of skin cancer from 1 in 250,000 to 1 in 150,000. Compare the clinical and statistical significance of this result.

Question 14

Use the following information for following questions:. These two headlines are on the same topic.
Headline A: Children who view advertisements for fast food dramatically increase their risk of becoming
obese adolescents, a new study suggests.
Headline B: Viewing advertisements for fast food leads to childhood obesity, a new study finds.
Was the study referenced most likely a controlled experiment or an observational study? Explain.

Question 15

A publisher is considering publishing a new magazine about environmentally-friendly living in the city and plans to gage interest in the magazine using potential consumers. Company researchers want to measure whether there is a difference in opinion between the new magazine and the competing publication. Company researchers believe that consumer reaction to the new magazine will depend on age so they decide to block on age. To do this, they create blocks for consumers between the ages 18-24 years, 25-32 years, 33-45 years, and 46 years and older. They then randomly select two of the blocks to read the first issue of the new magazine and the other two blocks to read a similar competing publication. Following the test, participants respond to a questionnaire about the magazine they read. Is this an effective design for the study? If not, describe an improvement.

Question 16

List three factors that affect the statistical power of a test. Be sure to list the factor over which researchers actually have some control.

Question 17

Use the following information for following questions:. Which treatment is most effective at
treating bathroom mildew: water mixed with vinegar, ammonia, or soap? In a study, researchers randomly
assigned 55 similar tile samples with similar amounts of mildew to one of three groups. Depending on
which group they were assigned to, each tile sample received a home remedy of water mixed with
vinegar, ammonia, or soap. Afterwards, each tile sample was examined and any remaining mildew was
measured. Researchers found that a soap and water mixture produced better results than both vinegar and
ammonia.
Is this a controlled experiment or an observational study? Explain.

Question 18

The city council of a moderate size city wants to gather input from the citizens of the city on the proposed expansion to the local airport. It has been decided that a stratified sampling plan would be the best way to get the desired information because opinions within the strata are likely to be similar. What would be a reasonable way to stratify the population?

Question 19

selected office for each of the twelve months prior to the exercise program and then for each of the
twelve months after the exercise program is initiated. The "before" and "after" expenses are
compared on a month-to-month basis. Which test design would be the most appropriate for this
scenario?
Describe a situation where a systematic sampling plan would be appropriate.

Question 20

selected office for each of the twelve months prior to the exercise program and then for each of the
twelve months after the exercise program is initiated. The "before" and "after" expenses are
compared on a month-to-month basis. Which test design would be the most appropriate for this
scenario?
Describe one benefit to a cluster sampling plan.

Question 21

Use the following information to answer questions (5) - (7). A tire manufacturer has made some
modifications to its most popular tire and wants to see if the tread on the modified tire will last
longer than the original tire. Because there is much variation in the way people drive, the
manufacturer decides to use blocking to reduce this variation. Twenty cars will be used to test the
tires. Ten cars are randomly selected to receive an original tire on the right rear wheel and a
modified tire on the left rear wheel. The remaining ten cars will receive an original tire on the left
rear wheel and a modified tire on the right rear wheel. Each car will then be driven 10,000 miles and
the amount of wear recorded for each wheel.
Is this a correct use of blocking?

A)Yes
B)No

Question 22

Which of the following statements is not true about a systematic sampling plan?

A)A systematic sampling plan divides the population into mini-populations that will have lower variability.
B)With systematic sampling, objects from the population are sampled at regular intervals.
C)Systematic sampling works best when objects are received in sequence during a specific time period and the characteristic of interest can be reasonably assumed to be randomly mixed during
The time period in which the data will be collected.
D)All of the above statements are true for a systematic sampling plan.

Question 23

Use the following information to answer questions (5) - (7). A tire manufacturer has made some
modifications to its most popular tire and wants to see if the tread on the modified tire will last
longer than the original tire. Because there is much variation in the way people drive, the
manufacturer decides to use blocking to reduce this variation. Twenty cars will be used to test the
tires. Ten cars are randomly selected to receive an original tire on the right rear wheel and a
modified tire on the left rear wheel. The remaining ten cars will receive an original tire on the left
rear wheel and a modified tire on the right rear wheel. Each car will then be driven 10,000 miles and
the amount of wear recorded for each wheel.
Was the study described above most likely an observational study or a controlled experiment?

A)Observational study because the researcher decided which car received which type of tire.
B)Observational study because the tires were not a random sample.
C)Experimental because the researchers placed both types of tires on each car, randomly assigning one type of tire to the right side and the other type to the left side.
D)Experimental because the researcher could not control how fast each car was driven.

Question 24

Use the following information for following questions:. Which treatment is most effective at
treating carpet stains: vinegar, ammonia, or hydrogen peroxide? In a study, researchers randomly assigned
55 carpet samples with identical stains to one of three groups. Depending on which group they were
assigned to, each carpet sample received a home remedy of water mixed with vinegar, ammonia, or
hydrogen peroxide. Afterwards, each carpet sample was examined and any remaining stain was measured.
Researchers found that a vinegar and water mixture produced better results than both ammonia and
hydrogen peroxide.
Choose the statement that restates the conclusion of the study in terms of a cause-and-effect conclusion.

A)A water and vinegar mixture effectively treats carpet stains compared to ammonia and hydrogen peroxide.
B)People who use water and vinegar to treat carpet stains will have fewer visible carpet stains.
C)A water and ammonia mixture effectively treats carpet stains compared to ammonia and hydrogen peroxide.
D)The type of treatment received is associated with the amount of stain removed.

Question 25

A coin collector has over 54 books containing varying number of coins of various denominations. He is very interested in knowing the value of the collection, but does not want to take the time to look up the value of each coin in the collection. He decides to randomly select 4 books and determines the value of each coin in each of the 4 books by looking up the coin in an online pricing book. What kind of sampling does this illustrate?

A)Systematic
B)Stratified
C)Cluster
D)Random sampling

Question 26

In order to estimate the average amount of money due on 484 open accounts, the accountant at a large manufacturing company randomly selects 25 open accounts to audit. What kind of sampling does this illustrate?

A)Systematic
B)Stratified
C)Cluster
D)Random sampling

Question 27

The quality control

A)A cluster sample of all cans filled between 8:00 am and 9:00 am and between 4:00 pm and 5:00 pm.
B)A simple random sample of cans filled before 12:00 pm.
C)A systematic sample of every 50th can throughout the day.
D)A simple random sample of cans filled after 12:00 pm.

Question 28

Which of the following is not a benefit of a stratified sampling plan?

A)Members of a stratum, or similar group, are likely to respond the same, which lead to results with lower variability.
B)Increased precision
C)Statistics from a stratum will reflect the parameters of the population as a whole.
D)All of the above are benefits of a stratified sampling plan.

Question 29

The city council of a moderate size city wants to gather input from the citizens of the city on the proposed expansion to the local airport. It has been decided that a stratified sampling plan would be the best way to get the desired information because opinions within the strata are likely to be similar. Which method of stratifying seems to be the most reasonable for this situation?

A)Stratify by gender.
B)Stratify by age.
C)Stratify by distance from the airport.
D)Stratify by income.

Question 30

Which of the following is not an important principle that should always be kept in mind when reading research articles containing statistical research results?

A)Don't rely solely on the conclusions of any single paper
B)Be wary of conclusions based on very complex statistical or mathematical models.
C)Stick to peer-reviewed journals.
D)All of the above are important principles.

Question 31

Use the following information for following questions:. A researcher wonders whether speed of
service at a diner is affected by whether a male customer is wearing a suit jacket. The researcher used the
following study design to collect data: The researcher chose five diners in a large city and recorded the
number of male customers who wore a suit jacket during a two week period. He also records how long it
took a waiter or waitress to address the customer. He finds that male customers who wear suit jackets
were addressed by the wait staff faster than male customers who did not wear a suit jacket.
Choose the statement that correctly explains why we can or cannot make a cause-and-effect conclusion.

A)This was an experimental study so we conclude that wearing a suit jacket caused a male customer to be addressed faster.
B)The male customers (and diners) were not selected from a larger population, so we cannot conclude that there was a cause-and-effect relationship.
C)This was an observational study.Since random assignment was not used, we cannot conclude that getting addressed faster was caused by wearing a suit jacket.
D)Since this was a controlled observational study we can conclude that there was a cause-and-effect relationship.

Question 32

Which of the following is not a primary factor that affects the power of a test?

A)The size of the true difference between treatment groups
B)Natural variability within the population
C)The sample standard deviation
D)Sample size

Question 33

Suppose a sociologist is interested in finding out if there is an association between gender and opinions on human cloning. Which test design would be most appropriate for this scenario?

A)Two-sample t-test
B)Chi-square
C)Paired t-test
D)ANOVA

Question 34

Suppose it was reported on the news that a recent study concluded that the probability that you will get brain cancer if you use a cell phone doubled from 1 in 460,000 to 1 in 230,000. Choose the statement that best summarizes the significance of this result.

A)Although this result may have statistical significance, it does not have clinical significance since the probability that you will get brain cancer if you use cell phone is still so small that it is
Unlikely to have a meaningful effect on lives.
B)Many would say that this result has both clinical and statistical significance because the probability more than doubled and this result could have a significant impact on lives.
C)Many would say that this result does not have clinical or statistical significance because the probabilities are so small that they are meaningless.
D)Although this result may have clinical significance, it does not have statistical significance since the probability that you will get brain cancer if you use a cell phone is still so small that it is
Unlikely to have a meaningful effect on lives.

Question 35

The personnel manager of a corporation wants to estimate, for one year, the total number of days used for sick leave among all 116 plants in his firm. The 116 plants are divided into 30 "small" plants, 45 "medium" plants, and 41 "large" plants. He decides to randomly select 40 employees from each of the three size of plants. What kind of sampling does this illustrate?

A)Systematic
B)Stratified
C)Cluster
D)Random sampling

Question 36

Suppose a gumball manufacturer decides to inspect every twenty-fifth gumball for defects. What kind of sampling does this illustrate?

A)Systematic
B)Stratified
C)Cluster
D)Random Sampling

Question 37

Use the following information for following questions:. A researcher wonders whether speed of
service at a diner is affected by whether a male customer is wearing a suit jacket. The researcher used the
following study design to collect data: The researcher chose five diners in a large city and recorded the
number of male customers who wore a suit jacket during a two week period. He also records how long it
took a waiter or waitress to address the customer. He finds that male customers who wear suit jackets
were addressed by the wait staff faster than male customers who did not wear a suit jacket.
Choose the statement that correctly explains why we can or cannot generalize these results to a larger population.

A)This was an observational study so results can be generalized to a larger population.
B)The male customers (and diners) were not selected from a larger population, so the results cannot be generalized beyond the sample.
C)The male customers were randomly selected to participate in the study so the results can be generalized to the larger population.
D)The male customers were randomly assigned to wear a suit jacket so the results cannot be generalized to beyond the sample.

Question 38

Use the following information for following questions:. Which treatment is most effective at
treating carpet stains: vinegar, ammonia, or hydrogen peroxide? In a study, researchers randomly assigned
55 carpet samples with identical stains to one of three groups. Depending on which group they were
assigned to, each carpet sample received a home remedy of water mixed with vinegar, ammonia, or
hydrogen peroxide. Afterwards, each carpet sample was examined and any remaining stain was measured.
Researchers found that a vinegar and water mixture produced better results than both ammonia and
hydrogen peroxide.
Was this a controlled experiment or an observational study?

A)Experimental because researchers determined, through randomized assignment, which treatment each carpet sample received
B)Experimental because researchers could not determine how much of the stain was removed
C)Observational study because researchers determined which treatment each carpet sample received
D)Observational study because the carpet samples were not a random sample

Question 39

Use the following information to answer questions (5) - (7). A tire manufacturer has made some
modifications to its most popular tire and wants to see if the tread on the modified tire will last
longer than the original tire. Because there is much variation in the way people drive, the
manufacturer decides to use blocking to reduce this variation. Twenty cars will be used to test the
tires. Ten cars are randomly selected to receive an original tire on the right rear wheel and a
modified tire on the left rear wheel. The remaining ten cars will receive an original tire on the left
rear wheel and a modified tire on the right rear wheel. Each car will then be driven 10,000 miles and
the amount of wear recorded for each wheel.
Which test design would be most appropriate for this scenario?

A)Two-sample z-test
B)Paired z-test
C)Two-sample t-test
D)Paired t-test

Question 40

Scientists were interested in determining if the amount of nicotine present in tobacco leaves is related to the amount of water received by the plants. In a greenhouse, a total of 120 tobacco plants were selected. During the growing season, 30 plants received the normal amount of water, 30 plants received 75% of the normal amount of water, 30 plants received 50% of the normal amount of water, and 30 plants received 25% of the normal amount of water. At the end of the growing season, one leaf was selected from each plant and the amount of nicotine present was recorded for each. Researchers determined that leaves from tobacco plants receiving the normal amount of water during the growing season had more nicotine than leaves from tobacco plants receiving less water. For this experiment, identify the response and treatment variables.

A)Response: Amount of nicotine in leaf.Treatment: Normal amount of water.
B)Response: Normal amount of water.Treatment: Amount of nicotine in leaf.
C)Response: Amount of nicotine in leaf.Treatment: Amount of water received by the plant.
D)Response: Amount of water received by the plant.Treatment: Amount of nicotine in leaf.

Question 41

A small study was conducted on a new procedure for treating atrial fibrillation. The study involved a new way to perform ablation surgery. One method currently being used had a success rate of only 50% in preventing additional episodes of atrial fibrillation within one year. The new method of performing ablation surgery was performed on 8 patients and 6 of the 8 patients did not suffer additional episodes of atrial fibrillation within one year. Choose the statement that best summarizes the significance of this result.

A)Many people would say that this result has both clinical and statistical significance because the probability of success increases from 50% to 75% and the result could have significant impact on
Lives.
B)Although this result may have clinical significance, it does not have statistical significance because the sample size is so small.
C)Although this result may have statistical significance, it does not have clinical significance because the sample size is so small.
D)Although this result may have statistical significance, it does not have clinical significance because the sample was not randomly selected.

Question 42

The quality control

A)A systematic sample of every 50th can throughout the day.
B)A simple random sample of cans filled after 12:00 pm.
C)A cluster sample of all cans filled between 8:00 am and 9:00 am and between 4:00 pm and 5:00 pm.
D)A simple random sample of cans filled before 12:00 pm.

Question 43

Which of the following statements are true concerning meta-analysis?

A)A meta-analysis considers all studies done to test a particular treatment and tries to reconcile different conclusions, attempting to determine whether other factors played a role in the reported
Outcomes.
B)Meta-analysis is the practice of stating hypotheses after first looking at the data.
C)Meta-analysis is used to prove clinical significance but not statistical significance.
D)Meta-analysis is used to prove statistical significance but not clinical significance.

Question 44

A coin collector has over 54 books containing varying number of coins of various denominations. He is very interested in knowing the value of the collection, but does not want to take the time to look up the value of each coin in the collection. He decides to randomly select 4 books and determines the value of each coin in each of the 4 books by looking up the coin in an online pricing book. What kind of sampling does this illustrate?

A)Systematic
B)Stratified
C)Cluster
D)Random sampling

Question 45

Use the following information to answer questions (5) - (7). A tire manufacturer has made some
modifications to its most popular tire and wants to see if the tread on the modified tire will last
longer than the original tire. Because there is much variation in the way people drive, the
manufacturer decides to use blocking to reduce this variation. Twenty cars will be used to test the
tires. Ten cars are randomly selected to receive an original tire on the right rear wheel and a
modified tire on the left rear wheel. The remaining ten cars will receive an original tire on the left
rear wheel and a modified tire on the right rear wheel. Each car will then be driven 10,000 miles and
the amount of wear recorded for each wheel.
Was the study described above most likely an observational study or a controlled experiment?

A)Experimental because the researchers placed both types of tires on each car, randomly assigning one type of tire to the right side and the other type to the left side.
B)Experimental because the researcher could not control how fast each car was driven.
C)Observational study because the researcher decided which car received which type of tire.
D)Observational study because the tires were not a random sample.

Question 46

The personnel manager of a corporation wants to estimate, for one year, the total number of days used for sick leave among all 116 plants in his firm. The 116 plants are divided into 30 "small" plants, 45 "medium" plants, and 41 "large" plants. He decides to randomly select 40 employees from each of the three size of plants. What kind of sampling does this illustrate?

A)Systematic
B)Stratified
C)Cluster
D)Random sampling

Question 47

Many landfills and dumps in the United States contain toxic materials. To see what proportion of the landfill contains toxic materials, the landfill is divided into 10,000 square grids that are each 10 feet by 10 feet square. After selecting one square grid at random to test for toxic materials, every five hundredth grid after that is selected for testing. What kind of sampling does this illustrate?

A)Systematic
B)Stratified
C)Cluster
D)Random sampling

Question 48

Use the following information for following questions:. Often college students taking an
introductory course in psychology are required to participate in research experiments. One experiment
was performed to see if using colored paper increased reading comprehension. One hundred students
enrolled in an introductory college psychology course volunteered to participate in the study. Fifty of the
students were randomly chosen to read a chapter in a psychology test that was printed on yellow paper
and the remaining fifty students were given the same chapter to read printed on white paper. After
reading the chapter, each student was asked to answer a series of questions to test his/her comprehension.
The results indicated that those students reading the chapter printed on yellow paper tended to have higher
comprehension scores than those students reading the chapter printed on white paper.
Choose the statement that correctly explains why we can or cannot generalize these results to a larger population.

A)This was an observational study so the results can be generalized to a larger population.
B)The participants were randomly assigned to a paper color, so the results can be generalized to a larger population.
C)The participants were randomly selected, so the results can be generalized to a large population.
D)The participants were not selected from a larger population so the results cannot be generalized beyond the sample.

Question 49

In order to estimate the average amount of money due on 484 open accounts, the accountant at a large manufacturing company randomly selects 25 open accounts to audit. What kind of sampling does this illustrate?

A)Systematic
B)Stratified
C)Cluster
D)Random sampling

Question 50

The city council of a moderate size city wants to gather input from the citizens of the city on the proposed expansion to the local airport. It has been decided that a stratified sampling plan would be the best way to get the desired information because opinions within the strata are likely to be similar. Which method of stratifying seems to be the most reasonable for this situation?

A)Stratify by gender.
B)Stratify by age.
C)Stratify by distance from the airport.
D)Stratify by income.

Question 51

Which of the following statements is true about a cluster sampling plan?

A)Members of a cluster are likely to respond the same, which leads to results with lower variability.
B)With cluster sampling, objects from the population are sampled at regular intervals.
C)A cluster sampling plan is often used for exit polls and quality control studies.
D)Cluster sampling can make it easier to access very large populations.

Question 52

Use the following information for following questions:. Often college students taking an
introductory course in psychology are required to participate in research experiments. One experiment
was performed to see if using colored paper increased reading comprehension. One hundred students
enrolled in an introductory college psychology course volunteered to participate in the study. Fifty of the
students were randomly chosen to read a chapter in a psychology test that was printed on yellow paper
and the remaining fifty students were given the same chapter to read printed on white paper. After
reading the chapter, each student was asked to answer a series of questions to test his/her comprehension.
The results indicated that those students reading the chapter printed on yellow paper tended to have higher
comprehension scores than those students reading the chapter printed on white paper.
Choose the statement that correctly explains why we can or cannot make a cause-and-effect conclusion.

A)This was an observational study so we cannot conclude that reading comprehension increases when reading text printed on yellow paper.
B)The participants were not selected from a larger population so we cannot conclude a cause-and- effect relationship.
C)Since this was a controlled observational study, we can conclude there was a cause-and-effect relationship.
D)This was an experimental study so we conclude that reading comprehension increases when reading from text printed on yellow paper, but the results cannot be generalized beyond the
Sample.

Question 53

Use the following information to answer questions (1) - (3). Scientists were interested in determining if
the amount of nicotine present in tobacco leaves is related to the amount of water received by the plants.
In a greenhouse, a total of 120 tobacco plants were selected. During the growing season, 30 plants were
randomly assigned to receive the normal amount of water, 30 plants received 75% of the normal amount
of water, 30 plants received 50% of the normal amount of water, and 30 plants received 25% of the
normal amount of water. At the end of the growing season, one leaf was selected at random from each
plant and the amount of nicotine present was recorded for each. Researchers determined that leaves from
tobacco plants receiving the normal amount of water during the growing season had more nicotine than
leaves from tobacco plants receiving less water.
Choose the statement that restates the conclusions of the study in terms of cause-and-effect conclusion.

A)Reduced amounts of water during the growing season is associated with a decrease in the amount of nicotine.
B)Normal amounts of water during the growing season produced less nicotine in tobacco leaves than reduced amounts of water.
C)Normal amounts of water during the growing season produced more nicotine in tobacco leaves than reduced amounts of water.
D)The amount of water received by tobacco plants during the growing season does not affect the amount of nicotine in the tobacco leaves.

Question 54

Use the following information to answer questions (5) - (7). A tire manufacturer has made some
modifications to its most popular tire and wants to see if the tread on the modified tire will last
longer than the original tire. Because there is much variation in the way people drive, the
manufacturer decides to use blocking to reduce this variation. Twenty cars will be used to test the
tires. Ten cars are randomly selected to receive an original tire on the right rear wheel and a
modified tire on the left rear wheel. The remaining ten cars will receive an original tire on the left
rear wheel and a modified tire on the right rear wheel. Each car will then be driven 10,000 miles and
the amount of wear recorded for each wheel.
Is this a correct use of blocking?

A)Yes
B)No

Question 55

Use the following information to answer questions (5) - (7). A tire manufacturer has made some
modifications to its most popular tire and wants to see if the tread on the modified tire will last
longer than the original tire. Because there is much variation in the way people drive, the
manufacturer decides to use blocking to reduce this variation. Twenty cars will be used to test the
tires. Ten cars are randomly selected to receive an original tire on the right rear wheel and a
modified tire on the left rear wheel. The remaining ten cars will receive an original tire on the left
rear wheel and a modified tire on the right rear wheel. Each car will then be driven 10,000 miles and
the amount of wear recorded for each wheel.
Which test design would be most appropriate for this scenario?

A)Two-sample t-test
B)Paired t-test
C)Two-sample z-test
D)Paired z-test

Question 56

Use the following information to answer questions (1) - (3). Scientists were interested in determining if
the amount of nicotine present in tobacco leaves is related to the amount of water received by the plants.
In a greenhouse, a total of 120 tobacco plants were selected. During the growing season, 30 plants were
randomly assigned to receive the normal amount of water, 30 plants received 75% of the normal amount
of water, 30 plants received 50% of the normal amount of water, and 30 plants received 25% of the
normal amount of water. At the end of the growing season, one leaf was selected at random from each
plant and the amount of nicotine present was recorded for each. Researchers determined that leaves from
tobacco plants receiving the normal amount of water during the growing season had more nicotine than
leaves from tobacco plants receiving less water.
For this experiment, identify the response and treatment variables.

A)Response: Amount of nicotine in leaf.Treatment: Amount of water received by the plant.
B)Response: Amount of water received by the plant.Treatment: Amount of nicotine in leaf.
C)Response: Amount of nicotine in leaf.Treatment: Normal amount of water.
D)Response: Normal amount of water.Treatment: Amount of nicotine in leaf.

Question 57

Choose the statement that best describes the power of a test.

A)The power of a test is the probability that the null hypothesis will be accepted when it is true.
B)The power of a test is the probability that the alternative hypothesis will be rejected when it is false.
C)The power of a test is the probability that the null hypothesis will be rejected when it is false.
D)None of these statements describes the power of a test.

Question 58

Which statement is not true about randomized block designs?

A)Each block should have objects in all treatment and control groups.
B)A block consists of objects that are similar on one or more variables.
C)Blocks are randomly assigned to each of the treatment and control groups.
D)All of the statements are true.

Question 59

Which of the following statements is true about a stratified sampling plan?

A)In stratified sampling, objects in the same stratum are as varied as possible.
B)Members of the same stratum are likely to respond the same, which leads to results with lower variability.
C)In stratified sampling, several strata are randomly selected and data is collected on every member of the selected strata.
D)Stratified sampling works best when objects are received in sequence during a specific time period and the characteristic of interest can be reasonably assumed to be randomly mixed during
The time period in which the data will be collected.

Question 60

Use the following information to answer questions (1) - (3). Scientists were interested in determining if
the amount of nicotine present in tobacco leaves is related to the amount of water received by the plants.
In a greenhouse, a total of 120 tobacco plants were selected. During the growing season, 30 plants were
randomly assigned to receive the normal amount of water, 30 plants received 75% of the normal amount
of water, 30 plants received 50% of the normal amount of water, and 30 plants received 25% of the
normal amount of water. At the end of the growing season, one leaf was selected at random from each
plant and the amount of nicotine present was recorded for each. Researchers determined that leaves from
tobacco plants receiving the normal amount of water during the growing season had more nicotine than
leaves from tobacco plants receiving less water.
Was this an observational study or a controlled experiment?

A)Observational study because the plants were not a random sample.
B)Observational study because the researchers determined how much water each group of plants would receive.
C)Experimental because researchers determined, through randomized assignment, which plants belonged to which treatment group.
D)Experimental because the researchers could not control the amount of nicotine in the plants.