AP STATS Unit III Experiments and Observational Studies

Suppose you wish to compare the average class size of mathematics classes to the average class size of English classes in your high school. Which is the most appropriate technique for gathering the needed data?

• Census

• Sample Survey

• Experiment

• Observational Study

• None of these methods is appropriate

Two studies are run to compare the experiences of families living in high-rise public housing to those of families living in townhouse subsidized rentals. The first study interviews 25 families who have been in each government program for at least 1 year, while the second randomly assigns 25 families to each program and interviews them after 1 year later. Which of the following is a true statement?

• Both studies are observational students because of the time and period involved.

• Both studies observational studies because there are no control groups.

• The first study is an observational study, while the second is an experiment.

• The first study is an experiment, while the second is an observational study.

• Both studies are experiments.

A study is made to determine whether taking AP Statistics in high school helps students achieve higher GPAs when they go to college. In comparing records of 200 college students, half of whom took AP Statistics in high school, it is noted that the average college GPA is higher for those 100 students who took AP Statistics than for those who did not. Based on this study, guidance counselors begin recommending AP Statistics for college bound students. Which of the following is incorrect?

• While this study indicates a relation, it does not prove causation.

• There could well be a confounding variable responsible for the seeming relationship.

• Self-selection here makes drawing the counselors’ conclusion difficult.

• A more meaningful study would be to compare an SRS from each of the two groups of 100 students.

• This is an observational study, not an experiment.

When the estrogen-blocking drug tamoxifen was first introduced to beat breast cancer, there was concern that it would cause osteoporosis as a side effect. To test this concern, cancer subjects were randomly selected and given tamoxifen, and their bone density was measured before and after treatment. Which of the following is a true statement?

• This study was an observational study.

• This study was a sample survey of randomly selected cancer patients.

• This study was an experiment in which the subjects were used as their own controls.

• With the given procedure, there cannot be a placebo effect.

• Causation cannot be concluded without knowing the survival rates.

In designing an experiment, blocking is used

• To reduce bias.

• To reduce variation.

• As a substitute for a control group.

• As a first step in randomization.

• To control the level of the experiment.

Is hot oatmeal with fruit or a Western omelet with home fries a more satisfying breakfast? Fifty volunteers are randomly split into two groups. One group is fed oatmeal with fruit, while the other is fed Western omelets with home fries. Each volunteer then rates his/her breakfast on a one to ten scale for satisfaction. If the Western omelet with home fries receives a substantially higher average score, what is a reasonable conclusion?

• In general, people find Western omelette with home fries more satisfying for breakfast than hot oatmeal with fruit.

• There is no reasonable conclusion because the subjects were volunteering rather than being randomly selected from the general population.

• There is no reasonable conclusion because of the small size of the sample.

• There is no reasonable conclusion because blinding was not used.

• There is no reasonable conclusion because there are too many possible confounding variables such as age, race, and ethnic background of the individual volunteers and season when the study was performed.

Which of the following is not important in the design of experiments?

• Control of confounding variables

• Randomization in assigning subjects to different treatments

• Replication of the experiment using sufficient numbers of subjects

• Care in observing without imposing change

• Isolating variability due to differences between blocks.

A study showed that persons who ate two carrots a day had significantly better eyesight than those who ate less than one carrot a week. Which of the following statements is (are) correct?

I. This study provides evidence that eating carrots contributes to better eyesight.

II. The general health consciousness of people who eat carrots could be a confounding variable.

III. This is an observational study and not an experiment.

• I only

• II only

• I and II only

• II and III only

• I, II, and III

Which of the following is true of an experiment but not of an observational study?

• A cause-and-effect relationship can be more easily inferred.

• The cost of conducting it is excessive.

• More advanced statistics are needed for analysis after the data are gathers.

• By law, the subjects need to be informed that they are part of a study.

• Possible confounding variables are more difficult to control.

Consider the following studies being run by three different nursing home establishments.

I. One nursing home has pets brought in for an hour every day to see if patient morale improved.

II. One nursing home allows hourly visits every day by kindergarten children to see if patient morale is improved.

III. One nursing home administers antidepressants to all patients to see if patient morale is improved.

Which of the following is true?

• None of these studies uses randomization.

• None of these studies uses control groups.

• None of these studies uses blinding.

• Important information can be obtained from all these studies, but none will be able to establish causal relationships.

• All of the above.