ch. 5 practice mc

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

biased, overstating the effectiveness of the diet.

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

confounding

The feed they get is not the only factor affecting the rate at which pigs gain weight. Genetic differences also affect weight gain. It is likely that the pigs in litter A are genetically different from the pigs in litter B, since the two litters have different mothers. Since the farmer is only interested in determining which brand of pellets is better, the study suffers from

confounding

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

creates approximately equal groups for comparison.

A stratified random sample is appropriate when

The population can be subdivided into strata according to some categorical variable which we believe has an effect on the response variable. Differences between the strata are much larger than differences within the strata.

A sportswriter wants to know how strongly Lafayette residents support the local minor league baseball team, the Lafayette Leopards. She stands outside the stadium before a game and interviews the first 20 people who enter the stadium. The newspaper asks you to comment on their survey of local opinion. You say:

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

The feed they get is not the only factor affecting the rate at which pigs gain weight. Genetic differences also affect weight gain. It is likely that the pigs in litter A are genetically different from the pigs in litter B, since the two litters have different mothers. If the farmer had fed Oinker 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 PigGrow pellets, then he would have been using

a randomized block design

A sportswriter wants to know how strongly Lafayette residents support the local minor league baseball team, the Lafayette Leopards. She stands outside the stadium before a game and interviews the first 20 people who enter the stadium. The population for this survey is

all people attending the game the day the survey was conducted.

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

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

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

distinguishes a treatment effect from the effects of confounding variables.

A farmer wishes to determine which of two brands of baby pig pellets, Oinker or PigGrow, produces better weight gains. Two of his sows each give birth to litters of 10 pigs on the same day, so he decides to give the baby pigs in litter A only Oinker pellets, while the pigs in litter B will get only PigGrow pellets. After four weeks, the average weight gain for pigs in litter A is greater than the average weight gain for pigs in litter B. The farmer has conducted a(n)

experiment, but not completely randomized

The most important advantage of experiments over observational studies is that

experiments can provide evidence of causation.

The principle reason for replication in designing experiments is that it

reduces sampling variability

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

statistically significant

A farmer wishes to determine which of two brands of baby pig pellets, Oinker or PigGrow, produces better weight gains. Two of his sows each give birth to litters of 10 pigs on the same day, so he decides to give the baby pigs in litter A only Oinker pellets, while the pigs in litter B will get only PigGrow pellets. After four weeks, the average weight gain for pigs in litter A is greater than the average weight gain for pigs in litter B. The brand of pellets is

the explanatory variable.

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

--a convenience sample

A simple random sample of size n is defined to be

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

A block design.

Which of the following statements is true?

If we use another list of random digits to select the sample,......

A sportswriter wants to know how strongly Lafayette residents support the local minor league baseball team, the Lafayette Leopards. She stands outside the stadium before a game and interviews the first 20 people who enter the stadium. The sample for the survey is

the 20 ppl who gave the sports writer their opinion

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

which brand they prefer.