AP Stats Types of Studies

The web portal AOL places opinion poll questions next to many of its news stories. Simply click your response to join the sample. One of the questions in January 2008 was "Do you plan to diet this year?" More than 30,000 people responded, with 68% saying "Yes." You conclude that

• about 68% of Americans planned to diet in 2008

• the poll used a convenience sample, so the results tell us little about the population of all adults.

• the poll uses voluntary response, so the results tell us little about the population of all adults.

• the sample is too small to draw any conclusions.

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Can changing diet reduce high blood pressure? Vegetarian and low-salt diets are both promising. Men with high blood pressure are assigned at random to four diets: 1) normal diet with unrestricted salt, 2) vegetarian with unrestricted salt, 3) normal with restricted salt, 4) vegetarian with restricted salt. This experiment has

• one factor, the type of diet

• two factors, high blood pressure and type of diet

• two factors, normal/vegetarian diet and unrestricted/restricted salt

• three factors, men, high blood pressure, and type of diet

• four factors, the types of diets being compared

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A farmer is conducting an experiment to determine which variety of apple tree, Fuji or Gala, will produce more fruit in his orchard. The orchard is divided into 20 equally sized square plots. He has 10 trees of each variety and randomly assigns each tree to a separate plot in the orchard. What are the experimental unit(s) in the study?

• The trees

• The plots

• The apples

• The farmer

• The orchard

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Your statistics class has 30 students. You want to call an SRS of 5 students from your class to ask where they use a computer for the online quizzes. You label the student 01, 02, ..., 30. You enter the table of random digits at this line:

14459 26056 31424 80371 65103 62253 22490 61181

Your SRS contains the students listed:

• 14,45,92,60,56

• 14,31,03,10,22

• 14,03,10,22,22

• 14,03,10,22,06

• 14,03,10,22,11

A gardener wants to try different combinations of fertilizer (none, 1 cup, 2 cups) and mulch (none, wood chips, pine needles, plastic) to determine which combination produces the highest yield for a variety of green beans. He has 60 green bean plants to use in the experiment. If he wants an equal number of plants to be assigned to each treatment, how many plants will be assigned to each treatment?

• 1

• 3

• 4

• 5

• 12

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Two essential features of all statistically designed experiments are

• compare several treatments and use the double-blind procedure

• compare several treatments and use chance to assign subjects to treatments

• always have a placebo group and use the double-blind method

• use a block design and use chance to assign subjects to treatments

• use enough subjects and always have a control group

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Principal Rusk picks 75 students at a recent varsity football game to be used for the sample.  This is what type of sampling design?

• SRS
• Stratified
• Convenience
• Voluntary Response

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The most important advantage of experiments over observational studies is that

• Experiments are easier to carry out

• Experiments can draw better conclusions about causation

• Experiments reduce confounding

• Observational studies do not have random samples

The most important advantage of experiments over observational studies is that

• A) experiments are usually easier to carry out
• B)Experiments can usually give better evidence of causation
• C) Confounding cannot happen in experiments
• D) Observational studies cannot use random samples

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In order to perform an experiment using 60 members of a gym, I first divide the list of members into men and women because I feel that the results will be different based on gender. I then randomly choose 30 men and 30 women. I assign half of the men to the treatment group and half to the control group. I repeat this procedure with the women. This is an example of a:

• randomized comparative design
• blocking design
• matched pairs design
• double blind simple random sample

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