Exam 12: Experimental Design: Controlling Variation

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.

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.

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

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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.

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?

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

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?

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.

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?

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.

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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.

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?

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?

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

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?

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?

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.

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.