Chapter 4.2 & 4.3 Review MC
Researchers wish to determine if a new experimental medication will reduce the symptoms of allergy sufferers without the side effect of drowsiness. To investigate this question, the researchers randomly assigned 100 adult volunteers who suffer from allergies to two groups. They gave the new medication to the subjects in one group and an existing medication to the subjects in the other group. Forty-four percent of those in the treatment group and 28% of those in the control group reported a significant reduction in their allergy symptoms without any drowsiness Use Scenarion 4-8. Which of the following best describes the inferences the researchers can make based in his results?
They can make inferences about cause and effect, but not about the populations from which the samples were taken
Researchers wish to determine if a new experimental medication will reduce the symptoms of allergy sufferers without the side effect of drowsiness. To investigate this question, the researchers randomly assigned 100 adult volunteers who suffer from allergies to two groups. They gave the new medication to the subjects in one group and an existing medication to the subjects in the other group. Forty-four percent of those in the treatment group and 28% of those in the control group reported a significant reduction in their allergy symptoms without any drowsiness Use Scenarion 4-8. The experimental units are the
100 adult volunteers
Use Scenario 4-3. The simple random sample is
Bechhofer, Taylor, Weiss.
When controlled experiments are impractical or unethical, which of the following would be necessary to establish a cause-and-effect relation between two variables? a. Strong association between the variables. b. An association between the variables is observed in many different settings. c. The alleged cause is plausible. d. There is no other obvious variable whose effect is confounded with the explanatory variable in the study. e. All of the above.
E. All of the above.
In order to assess the effects of exercise on reducing cholesterol, a researcher took a random sample of fifty people from a local gym who exercised regularly and another random sample of fifty people from the surrounding community who did not exercise regularly. They all reported to a clinic to have their cholesterol measured. The subjects were unaware of the purpose of the study, and the technician measuring the cholesterol was not aware of whether or not subjects exercised regularly Use Scenario 4-5. Which of the following best describes the inferences the researcher can make based on his results?
He can make inferences about the populations from which the samples were taken, but not about cause and effect
A stratified random sample is appropriate when
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 farmer wishes to determine which of two brands of baby pig pellets, Kent or Moormans, 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 Kent pellets, while the pigs in litter B will get only Moormans 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. 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
a block design
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 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
cluster sampling
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
cluster sampling
The reason that blocking (as in a randomized block design) is sometimes used in experimentation is to
compensate for anticipated differences in the response variable for different values of a specified 'blocking" variable
A farmer wishes to determine which of two brands of baby pig pellets, Kent or Moormans, 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 Kent pellets, while the pigs in litter B will get only Moormans 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. Use Scenario 4-7. 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
Does caffeine improve exam performance? Suppose all students in the 8:30 section of a course are given a "treatment" (two cups of coffee) and all students in the 9:30 section are not permitted to have any caffeine before a mid-term exam. Use Scenario 4-6. Unfortunately, any systematic difference between the two sections on the exam might be due to the fact that the 8:30 and 9:30 classes have different instructors. This is an example of
confounding
The principle reason for the use of random assignment in designing experiments is that it
creates approximately equal groups for comparison
The principle reason for the use of controls in designing experiments is that it
distinguishes a treatment effect from the effects of confounding variables
In order to assess the effects of exercise on reducing cholesterol, a researcher took a random sample of fifty people from a local gym who exercised regularly and another random sample of fifty people from the surrounding community who did not exercise regularly. They all reported to a clinic to have their cholesterol measured. The subjects were unaware of the purpose of the study, and the technician measuring the cholesterol was not aware of whether or not subjects exercised regularly Use Scenario 4-5. This is a(n)
double blind experiment
In comparative trials in medicine, the placebo effect and subconscious bias on the part of the physicians evaluating treatment outcomes can be avoided by using
double-blind technique
Which of these statements about the table of random digits is true? A. Every row must have exactly the same number of 0's and 1's. b. In the entire table, there are exactly the same number of 0's and 1's. c. If you look at 100 consecutive pairs of digits anywhere in the table, exactly 1 pair is 00. d. All of these are true. e. None of these is true.
e. None of these is true
A farmer wishes to determine which of two brands of baby pig pellets, Kent or Moormans, 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 Kent pellets, while the pigs in litter B will get only Moormans 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. Use Scenario 4-7. The farmer has conducted a(n)
experiment, but not a completely randomized experiment
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
One hundred volunteers who suffer from severe depression are available for a study. Fifty are selected at random and are given a new drug that is thought to be particularly effective in treating severe depression. The other fifty are given an existing drug for treating severe depression. A psychiatrist evaluates the symptoms of all volunteers after four weeks in order to determine if there has been substantial improvement in the severity of the depression. The study would be double blind if
neither the volunteers nor the psychiatrist knew which treatment any person had received
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
nonresponse
Does caffeine improve exam performance? Suppose all students in the 8:30 section of a course are given a "treatment" (two cups of coffee) and all students in the 9:30 section are not permitted to have any caffeine before a mid-term exam. 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
randomized block design
The principle reason for replication in designing experiments is that it
reduces sampling variability
A public opinion poll in Ohio wants to determine whether or not registered voters in the state approve of a measure to ban smoking in all public areas. They select a simple random sample of fifty registered voters from each county in the state and ask whether they approve or disapprove of the measure. This is an example of a
stratified random sample
You plan to give a math achievement test to samples of 15 year-olds from both the U.S. and Korea in order to compare mathematics knowledge in the two countries. In each country, you will randomly choose 300 students from low-income families 400 students from middle-income families 200 students from high-income families The sample from Korea is a
stratified random sample
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
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
suffer from lack of realism
A farmer wishes to determine which of two brands of baby pig pellets, Kent or Moormans, 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 Kent pellets, while the pigs in litter B will get only Moormans 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. Use Scenario 4-7. The brand of pellets is
the explanatory variable
A farmer wishes to determine which of two brands of baby pig pellets, Kent or Moormans, 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 Kent pellets, while the pigs in litter B will get only Moormans 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. Use Scenario 4-7. The weight of the pigs after four weeks is
the response variable
In the late 1990's Scotland was considering independence from England. An opinion poll showed that 51% of Scots favored "independence." Another poll taken at the same time showed that only 34% favored being "separate" from England. The reason these results differ by so much is that
the wording of questions has a big effect on poll results.
Just before the presidential election of 1936, the magazine Literary Digest predicted—incorrectly, as it turned out—that Alf Landon would defeat Franklin Delano Roosevelt. Landon lost in a landslide. It turned out that the magazine had only polled its own subscribers, plus others from a list of automobile owners and a list of people who had telephone service. All three groups had higher than typical incomes during the Great Depression. This is an example of
undercoverage
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. Eight of the volunteers are men, and four are women. Half of the volunteers are to be given shark fin extract twice a day, and the other half are to be given a placebo twice a day. We wish to make sure that four men and two women are assigned to each of the treatments, so we decide to use a block design with the men forming one block and the women the other. A block design is appropriate in this experiment if
we believe men and women will respond differently to treatments.
Does caffeine improve exam performance? Suppose all students in the 8:30 section of a course are given a "treatment" (two cups of coffee) and all students in the 9:30 section are not permitted to have any caffeine before a mid-term exam. Use Scenario 4-6. Instead of giving all students in the 8:30 section two cups of coffee, students in the 8:30 section are randomly assigned to a treatment group (two cups of coffee) or a control group (two cups of decaffeinated coffee). The coffee is so bad that students cannot tell whether they are in the treatment or the control group. As it turns out, students in both groups do better on the exam than students in the 9:30 section, who weren't given anything. This could be the result of
the placebo effect
Are dogs better at tracking the movements of white objects or red objects? Fifteen experienced "disk dogs" who have been trained to catch flying disks in mid-air are given the chance to catch a bright red disk or a plain white disk. Each disk is thrown 10 times for each dog, with the sequence of disks (red or white) determined randomly. The proportion of red disks caught to the proportion of white disks caught is compared for each dog. This is an example of a
matched pairs design
Use Scenario 4-3. Which of the following statements is true?
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