Exam 12: Experimental Design: Controlling Variation

Use the following information to answer the question. A researcher wonders whether receiving a job offer is effected by whether an interviewee wears a red tie. The researcher used the following study design to collect data: The researcher chose five large companies in a large city and observed the tie color of all interviewees during a two week period. He also records whether the person was hired by the company. He finds that interviewees who wear red ties are more likely to be hired than interviewees who do not wear red ties. -Choose the statement that correctly explains 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 more than 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 the question. 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.

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

A bank manager is interested in the opinions of people who visit the bank on a typical day. The manager thinks that opinions of people who visit the bank in the morning could be different than those who visit later in the day and he does not want a biased sample. Describe a sampling method that is likely to result in an unbiased sample. Explain.

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

Describe one benefit to a cluster sampling plan.

Use the following information to answer the question. A researcher wonders whether receiving a job offer is effected by whether an interviewee wears a red tie. The researcher used the following study design to collect data: The researcher chose five large companies in a large city and observed the tie color of all interviewees during a two week period. He also records whether the person was hired by the company. He finds that interviewees who wear red ties are more likely to be hired than interviewees who do not wear red ties. -Choose the statement that correctly explains why we can or cannot make a cause- and- effect conclusion.

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

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.

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.

Suppose a snow blower manufacturer decides to inspect every seventh snow blower for paint defects. What kind of sampling does this illustrate?

Use the following information to answer the question. 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?

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

Asphodelus fistulosus, a noxious weed commonly known as onionweed, is considered an invasive species in New Mexico and can choke out other vegetation. To detect the presence of onionweed on public land, environmental researchers partition land into one acre parcels then randomly select a sample of parcels to be fully inspected for the presence of onionweed. What kind of sampling does this illustrate?

Suppose a sociologist reports that after analyzing data that he collected on the drinking habits of college students, he decided to test that hypothesis that there is no difference in the drinking habits of fourth year students and first year students. What research error has been committed by the sociologist?

Describe a situation where a systematic sampling plan would be appropriate.

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.

A ranch salad dressing manufacturer has developed a new recipe for its ranch dressing and is planning a consumer taste test. Researchers in the test kitchen want to measure whether there is a difference in consumer opinions between the old recipe and the new recipe. Company researchers believe that consumer reaction to the new dressing will depend on gender so they decide to block on gender. To do this, they create blocks for female adult consumers and male adult consumers. They then randomly assign subjects in each block to taste dressings using the new and old recipe. Following the taste test, participants respond to a questionnaire about the dressings they tasted. Is this an effective design for this study?

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