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Learn the difference between cluster sampling and stratified random sampling, key to reducing confounding, and design weaknesses in randomized paired comparison designs with repeated measures.
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Chapter 4 Potpourri
Surveys vs Experiments Eliminates selection bias
Sampling 1. What is the difference between the groups for cluster sampling and stratified random sampling?
Sampling • What is the difference between the groups for cluster sampling and stratified random sampling? Clusters: similar characteristics; each group is representative of population Stratified: different characteristics --level of income, political party
2. What is the key to reducing confounding in an experiment?
2. What is the key to reducing confounding in an experiment? Assign treatments at random to experimental units
3. Suppose pairs of identical twins agree to participate in an experiment to test the effect of salt on blood pressure. It is decided by a coin flip which of the twins will consume a high-salt diet and which will consume a low-salt diet. The response variable will be their blood pressure after ten weeks on the diet. This is an example of ___________.
3. Suppose pairs of identical twins agree to participate in an experiment to test the effect of salt on blood pressure. It is decided by a coin flip which of the twins will consume a high-salt diet and which will consume a low-salt diet. The response variable will be their blood pressure after ten weeks on the diet. This is an example of A. a completely randomized design B. a randomized paired comparison design (matched pairs) C. a randomized paired comparison design with repeated measures on the same subject D. stratification E. two-stage cluster sampling
3. Suppose pairs of identical twins agree to participate in an experiment to test the effect of salt on blood pressure. It is decided by a coin flip which of the twins will consume a high-salt diet and which will consume a low-salt diet. The response variable will be their blood pressure after ten weeks on the diet. This is an example of A. a completely randomized design B.a randomized paired comparison design (matched pairs) C. a randomized paired comparison design with repeated measures on the same subject D. stratification E. two-stage cluster sampling
4. When the effects of two variables on a response variable cannot be distinguished from each other, the variables are said to be __________.
4. When the effects of two variables on a response variable cannot be distinguished from each other, the variables are said to be A. biased B. blocked C. confounded D. stratified E. outliers
4. When the effects of two variables on a response variable cannot be distinguished from each other, the variables are said to be A. biased B. blocked C. confounded D. stratified E. outliers
5. To test a new skin rash drug, researchers decide to administer both the new drug and the standard drug, in random order, to each patient in the experimental study. That is, the researchers carrying out the study plan to use a randomized paired comparison design with repeated measures. What is the main weakness of this design?
5. To test a new skin rash drug, researchers decide to administer both the new drug and the standard drug, in random order, to each patient in the experimental study. That is, the researchers carrying out the study plan to use a randomized paired comparison design with repeated measures. What is the main weakness of this design? A. It did not use blocking. B. The resulting data would show evidence of too much within-treatment variability. C. The resulting data would show evidence of too much between-treatment variability. D. There was no control group. E. The effect of the first drug may not have worn off before the second drug was administered.
5. To test a new skin rash drug, researchers decide to administer both the new drug and the standard drug, in random order, to each patient in the experimental study. That is, the researchers carrying out the study plan to use a randomized paired comparison design with repeated measures. What is the main weakness of this design? A. It did not use blocking. B. The resulting data would show evidence of too much within-treatment variability. C. The resulting data would show evidence of too much between-treatment variability. D. There was no control group. E.The effect of the first drug may not have worn off before the second drug was administered.
6. Suppose you want to study the effect of calculator use on the mathematics course grade for sixth-grade students in a district’s single middle school. In the upcoming school year, the middle school will have a total of 500 sixth-grade students.
6. Suppose you want to study the effect of calculator use on the mathematics course grade for sixth-grade students in your district’s single middle school. In the upcoming school year, the middle school will have a total of 500 sixth-grade students. Now, suppose that you plan to ask each student whether he or she uses a calculator and then compare the mean mathematics course grade for each group. Is this an observational study or an experiment? Explain.
Suppose that you plan to ask each student whether he or she uses a calculator and then compare the mean mathematics course grade for each group. Is this an observational study or an experiment? Explain. It’s an observational study because the two treatments (using/not using a calculator) are not randomly assigned to the students.
7. Identify which type of sampling design is being used in each scenario. a. A school administrator randomly selects 12 classes from your school and then randomly selects 5 students from each class to study a school library issue.
7. Identify which type of sampling design is being used in each scenario. a. A school administrator randomly selects 12 classes from your school and then randomly selects 5 students from each class to study a school library issue. two-stage cluster sample
7. Identify which type of sampling design is being used in each scenario. b. A school administrator uses random numbers to select a sample of 60 students from the roster of students enrolled in your school.
7. Identify which type of sampling design is being used in each scenario. b. A school administrator uses random numbers to select a sample of 60 students from the roster of students enrolled in your school. simple random sample
c. A school administrator gets a sample of 60 students from your school by randomly selecting 15 freshmen, 15 sophomores, 15 juniors, and 15 seniors.
c. A school administrator gets a sample of 60 students from your school by randomly selecting 15 freshmen, 15 sophomores, 15 juniors, and 15 seniors. stratified random sample
d. A school administrator uses the roster of students enrolled in your school to select a sample of students by choosing a person randomly from among the first 20 and then taking every 20th name on the roster thereafter.
A school administrator uses the roster of students enrolled in your school to select a sample of students by choosing a person randomly from among the first 20 and then taking every 20th name on the roster thereafter. systematic sample with random start
8. Blocking will be effective if A. all units in one block receive the same treatment B. each subject receives all treatments C. units are grouped so that each block contains units that are different D. units are grouped so that each block contains units that are similar E. units are grouped so that each block is representative of the population
8. Blocking will be effective if A. all units in one block receive the same treatment B. each subject receives all treatments C. units are grouped so that each block contains units that are different D. units are grouped so that each block contains units that are similar E. units are grouped so that each block is representative of the population
9. What is the main purpose of random selection in a sample survey?
9. What is the main purpose of random selection in a sample survey? To reduce bias and get a representative sample from the population
10. Compared to simple random sampling, stratified sampling can help accomplish several goals. Which of these goals does it not advance? A. reduce the variability associated with a statistic such as the sample mean B. improve the precision of the results C. provide good information on each stratum D. make it unnecessary to use randomization E. make it easier to take a sample
10. Compared to simple random sampling, stratified sampling can help accomplish several goals. Which of these goals does it not advance? A. reduce the variability associated with a statistic such as the sample mean B. improve the precision of the results C. provide good information on each stratum D. make it unnecessary to use randomization E. make it easier to take a sample
11. There are two types of bias in sampling problems: bias due to the improper selection of sampling units and bias due to incorrect response or nonresponse. Which of these is least likely to help protect against bias? A. random selection of sampling units B. cluster sampling as compared to simple random sampling C. following up with those who do not respond to the initial survey D. designing clear and unambiguous questions E. constructing a good sampling frame
11. There are two types of bias in sampling problems: bias due to the improper selection of sampling units and bias due to incorrect response or nonresponse. Which of these is least likely to help protect against bias? A. random selection of sampling units B. cluster sampling as compared to simple random sampling C. following up with those who do not respond to the initial survey D. designing clear and unambiguous questions E. constructing a good sampling frame
