Stat Chap 4 Test

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

. C. statistically significant

A lurking variable is

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

In comparative trials in medicine, the placebo effect and subconscious bias

A. the double-blind technique.

A study of elementary school children, ages 6 to 11, finds a high positive correlation between shoe size x and score y on a test of reading comprehension. The observed correlation is most likely due to

A. the effect of a lurking variable, such as age.

One hundred volunteers who suffer from severe depression are available for a study. The factor in this study is

A. which treatment the volunteers receive

Which of the following statements about a randomized complete block design with two treatments is not true?

B. Block A is chosen randomly

Twelve people who suffer from chronic fatigue syndrome volunteer to take part in an experiment to see if shark fin extract will increase one's energy level.

B. we believe men and women will respond differently to treatments.

A double-blind experiment was conducted to evaluate the effectiveness of the Salk polio vaccine.

C. eliminate a possible source of bias.

One hundred volunteers who suffer from severe depression are available for a study. The study would be double blind if

C. neither the volunteers nor the psychiatrist knew which treatment any person had received.

The owner of a chain of supermarkets notices that there is a positive correlation between the sales of beer and the sales of ice cream over the course of the previous year. During seasons when sales of beer were above average, sales of ice cream also tended to be above average. Likewise, during seasons when sales of beer were below average, sales of ice cream also tended to be below average. Which of the following would be a valid conclusion from these facts?

D. It is likely that sales of both beer and ice cream are confounded with a lurking variable, such as seasonal variation in temperature.

An experiment compares the taste of a new spaghetti sauce this is called

D. matched pairs design

Are dogs better at tracking the movements of brightly colored objects? ex of a

D. matched pairs design.

Medical researchers are excited about a new cancer treatment that destroys tumors by cutting off their blood supply. To date, the treatment has only been tried on mice, but in mice it has been nearly 100% effective in eradicating tumors and appears to have no side effects. As evidence of the effectiveness of the new treatment in treating cancer in humans, these studies

D. suffer from lack of realism.

When controlled experiments are impractical or unethical, which of the following would be necessary to establish a cause-and-effect relation between two variables?

E. All of the above.

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

E. reduce variability arising from random assignment.

A candidate for mayor of Dallas calls 1,000 people chosen at random from the city telephone directory; 850 of them respond. What are the sampling frame and the sample in this example?

Sampling frame: the telephone directory. Sample: the 850 people who respond.

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

a. A block design.

A television station is interested in predicting whether voters in its viewing area are in favor of offshore drilling. It asks its viewers to phone in and indicate whether they support/are in favor of or are opposed to this practice. Of the 2241 viewers who phoned in, 1574 (70%) were opposed to offshore drilling. The viewers who phoned in are

a. a voluntary response sample.

The intended population for this survey is

a. all residents of Lafayette.

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.

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

a. distinguishes a treatment effect from the effects of confounding variables.

A local tax reform group polls the residents of the school district and asks the question, "Do you think the school board should stop spending taxpayers' money on non-essential arts programs in elementary schools?" The results of this poll are likely to

b. Underestimate support for arts programs because of nonsampling error.

To determine the proportion of each color of Peanut Butter M&M, you buy 10 1.69 ounce packages and count how many there are of each color. This is an example of

b. cluster sampling

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

c. Blocking

A stratified random sample is appropriate when

c. The population can be easily subdivided into groups according to some categorical variable, and the variable you are measuring is very similar within the groups but quite different between groups.

A simple random sample of size n is defined to be

c. a sample of size n chosen in such a way that every set of n units in the population has an equal chance to be the sample actually selected.

A simple random sample is

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

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.

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

An opinion research firm wants to find the country's reaction to a speech by a famous politician. They randomly select six states, then randomly select ten Zip Codes from each state. Fifty people from each Zip Code are randomly selected for the survey. This is an example of

multistage sampling.

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

stratified random sampling

For one kindergarten class in his district, a researcher determines which children already can read simple words and which children cannot upon entering kindergarten. The researcher

b. cannot conclude that being able to read before entering kindergarten is beneficial, as there may be confounding variables in this study.

The most important advantage of experiments over observational studies is that

b. experiments can give better evidence of causation.

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

confounding

Sportswear The sample for the survey is

d. the 20 people who gave the sportswriter their opinion

An experiment was conducted by some students to explore the nature of the relationship between a person's heart rate (measured in beats per minute) and the frequency at which that person stepped up and down on steps of various heights. Three rates of stepping and two different step heights were used. A subject performed the activity (stepping at one of the three stepping rates at one of the two possible heights) for three minutes. Heart rate was then measured at the end of this period. The variables "stepping rate" and "step height" are the

a. factors.

A marketing research firm wishes to determine if the adult men in Laramie, Wyoming, would be interested in a new upscale men's clothing store. From a list of all residential addresses in Laramie, the firm selects a simple random sample of 100 and mails a brief questionnaire to each. The chance that all 100 homes in a particular neighborhood in Laramie end up being the sample of residential addresses selected is

a. the same as for any other set of 100 residential addresses.

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.

A market research company wishes to find out whether the population of students at a university prefers brand A or brand B of instant coffee. A random sample of students is selected, and each one is asked to try brand A first and then brand B (or vice versa, with the order determined at random). They then indicate which brand they prefer. The response variable is

b. which brand they prefer.

4-3 Bechhofer, Brown, Ito The simple random sample is

c. Bechhofer, Taylor, Weiss.

In order to select a sample of undergraduate students in the United States, I select a simple random sample of four states. From each of these states, I select a simple random sample of two colleges or universities. Finally, from each of these eight colleges or universities, I select a simple random sample of 20 undergraduates. My final sample consists of 160 undergraduates. This is an example of

c. multistage sampling.

The principle reason for replication in designing experiments is that it

c. reduces sampling variability

4-3 Which of the following statements is true?

d. If we use another list of random digits to select the sample, the result obtained with the list actually used would be just as likely to be selected as any other set of three names.

A study sponsored by American Express Co. and the French government tourist office found that old stereotypes about French unfriendliness were not true. The respondents were more than 1000 Americans who have visited France more than once for pleasure over the past two years. The results of this study are probably

d. biased, overstating the extent to which the old stereotypes were not true.

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

d. creates approximately equal groups for comparison.

Frequently, telephone poll-takers call near dinner time—between 6 pm and 7 pm—because most people are at home them. This is an effort to avoid

d. nonresponse.

Simple random sampling

e. None of the above.

4-3 Which of these statements about the table of random digits is true?

e. None of these is true.

The essential difference between an experiment and an observational study is that

e. an experiment imposes treatments on the subjects, but an observational study does not.

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.