Stat Midterm Chapter 4

A stratified random sample addresses the same issues as which of the following experimental designs?

A. A block design.

A lurking variable is

A. a variable that is not among the variables studied but that affects the response variable.

A sportswriter wants to know how strongly Lafayette residents.... Use Scenario 4-1. The intended population for this survey is

A. all residents of Lafayette.

In order to assess the effects of exercise on reducing cholesterol... Use Scenario 4-5. This is a(n)

A. observational study.

You want to know the opinions of American school teachers.... Use Scenario 4-2. The sample is

A. the 1347 teachers who mail back the questionnaire.

. Use Scenario 4-5. Which of the following best describes the inferences the researcher can make based in his results?

B. He can make inferences about the populations from which the samples were taken, but not about cause and effect

A marine biologist wants to estimate the mean size of the barnacle Semibalanus balnoides on a stretch of rocky shoreline. To do so, he randomly selected twenty 10-cm. square plots and measured the size of every barnacle in each plot. This is an example of

B. cluster sampling.

The most important advantage of experiments over observational studies is that

B. experiments can give better evidence of causation.

We wish to choose a simple random sample of size three... Use Scenario 4-3. The simple random sample is

C. Bechhofer, Taylor, Weiss.

Which of the following is not a major principle of good design for all experiments?

C. Blocking

A simple random sample is

C. a sample that gives every possible sample of the same size the same chance to be selected.

If changes in a response variable are due to the effects of the explanatory variable as well as the effects of lurking variables, and we cannot distinguish between these effects, we are said to have

C. confounding.

The principle reason for replication in designing experiments is that it

C. reduces sampling variability.

In an experiment, an observed effect so large that it would rarely occur by chance is called

C. statistically significant.

Use Scenario 4-4. Another correct choice of labels for the 816 students is

D. Both (B) and (C) are correct.

Use Scenario 4-1. The newspaper asks you to comment on their survey of local opinion. You say:

D. This is a convenience sample. It will almost certainly overestimate the level of support among all Lafayette residents.

A farmer wishes to determine which of two brands of baby pig pellets.... Use Scenario 4-7. If the farmer had fed Kent pellets to an SRS of 5 pigs from litter A and an SRS of 5 pigs from litter B, with the remaining 10 pigs getting Moormans pellets, then he would have been using

D. a block design.

. In order to assess the opinion of students at the University of Minnesota on campus snow removal, a reporter for the student newspaper interviews the first 12 students he meets who are willing to express their opinion. The method of sampling used is

D. a convenience sample

The principle reason for the use of random assignment in designing experiments is that it

D. creates approximately equal groups for comparison.

We divide the class into two groups: first year students and others. We then take random samples from each group. This is an example of

D. stratified random sampling

You want to take an SRS of 50 of the 816 students.... Use Scenario 4-4. The first three students in your sample have labels

E. 400, 769, 335.

Simple random sampling

E. None of the above.

Use Scenario 4-6. Suppose half of the 8:30 students are randomly allocated to the treatment group (two cups of coffee), the other half to the control group (two cups of decaf). In addition, half of the 9:30 students are randomly allocated to the treatment group, the other half to the control group. This is an example of a

E. block design.

Does caffeine improve exam performance?..... Use Scenario 4-6. The response variable in this study is

E. exam performance.

An example of a nonsampling error that can reduce the accuracy of a sample survey is

E. many members of the sample cannot be contacted.

____ 30. The reason that blocking (as in a randomized block design) is sometimes used in experimentation is to

E. reduce variability arising from random assignment.

. The Bradley effect is a theory proposed to explain observed discrepancies between voter opinion polls and election outcomes in some elections where a white candidate and a non-white candidate run against each other. The theory proposes that some voters tend to tell pollsters that they are undecided or likely to vote for a non-white candidate, and yet, on election day, vote for the white opponent. This is an example of

E. response bias.

. A news release for a diet products company reports: "There's good news for the 65 million Americans currently on a diet." Its study showed that people who lose weight can keep it off. The sample was twenty graduates of the company's program who endorse it in commercials. The results of the study are probably

A. biased, overstating the effectiveness of the diet.

Use Scenario 4-7. The weight of the pigs after four weeks is

B. the response variable.

Use Scenario 4-1. The sample for the survey is

D. the 20 people who gave the sportswriter their opinion.