Exam 12: Experimental Design: Controlling Variation

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.

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.

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.

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?

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.

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.

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?

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.

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.

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.

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?

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

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

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?

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?

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?

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.

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?

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?

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