AnswersStatistics and ProbabilityExperimental Designs

Experimental Designs — Quiz Answers

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1
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Which of the following describes a randomized block design for this experiment?

A
The subjects are numbered 1–50 and these numbers are put into a random number generator. The first 25 random numbers, ignoring repeats, represent the subjects assigned to the new model group. The remaining 25 subjects will wear the original model of shoes.
B
The 50 subjects are grouped based on running ability. Twenty runners classify themselves as competitive runners and the remaining 30 classify themselves as recreational runners. For the competitive group, the runners’ names are written on equal-sized slips of paper and placed into a hat. The slips are shuffled, and the first 10 runners wear the new model of shoes and the other 10 wear the original model. The same procedure is used to assign the shoes to the recreational group.
C
The 50 subjects are paired based on running ability. The fastest two runners are paired together, the next fastest two, etc. For each pair of runners the researcher will flip a coin. If the coin lands on heads, then the first runner will receive the new model of shoes and the second will receive the original model. If the coin lands on tails, the first runner will receive the original model of shoes and the second runner will receive the new model of shoes.
D
The subjects’ names are written on equal-sized slips of paper and placed into a hat. A researcher then reaches in and pulls out 25 slips of paper. These subjects are assigned to the new model group. The remaining 25 subjects will be assigned to the original model group.
2
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Which of the following describes a completely randomized design for this experiment?

A
Volunteers are put together based on stress level in groups of two. For each group of two, a coin is flipped and if it is heads, then the first person is placed in the yoga group, and if it is tails, then the first person is placed in the meditation group. The other person will be placed in the other group. After one month, the stress levels between the two participants are measured and compared.
B
The volunteers are grouped based on their current stress level. The 30 volunteers with the highest level of reported stress are placed in one group and the remaining 30 volunteers are placed in another group. The therapist flips a coin and if it lands on heads, then the group with the highest stress levels will receive the yoga treatment. If it lands on tails, then this group will receive the meditation treatment. After one month, the stress levels will be compared between the two groups.
C
The volunteers’ names are all placed on equal-sized slips of paper and these slips are put into a hat. The therapist draws 30 slips of paper and the corresponding volunteers are placed into the yoga group. The remaining 30 volunteers are placed in the meditation group. After one month, the stress levels between the two groups are measured and compared.
D
The volunteers’ names are all placed on equal-sized slips of paper and these slips are put into a hat. After the hat is shaken, a slip of paper is drawn without replacement and the corresponding volunteer is placed in the yoga group. This is repeated until the yoga group has 30 volunteers. The remaining 30 volunteers are placed in the meditation group. After one month, the stress levels between the two groups are measured and compared.
3

Which of the following describes a randomized block design for this experiment?

A
There are six vehicles of each vehicle type: sedan, SUV, minivan, and truck. Each vehicle type is numbered 1–4, and these numbers are entered into a random number generator. The first two unique numbers selected will represent the group of vehicles that will receive tires with the new type of tread. The remaining 2 groups will receive tires with the original tread.
B
Each vehicle is numbered 1–24, and these numbers are put into a random number generator. The first 12 unique numbers represent the vehicles that will receive the tires with the new tread. The remaining 12 vehicles will receive the tires with the original tread.
C
There are six vehicles of each vehicle type: sedan, SUV, minivan, and truck. For each type, three vehicles will be randomly selected to receive tires with the new tread and the other three vehicles will receive tires with the original tread.
D
The vehicles will be put in groups of two based on the size of the vehicle, with the largest two put together, the next largest two, etc. For each of the 12 pairs, the largest vehicle will get tires with the original type of tread and the other vehicle in the pair will get the new type of tread.
4

Which of the following best describes the design for this experiment?

A
observational study
B
completely randomized design
C
matched pairs design
D
randomized block design
5

Is this a completely randomized design?

A
Yes, the plants were randomly assigned each treatment.
B
No, only spider plants were used.
C
Yes, the plants received the same amount of soil, water, and light.
D
No, the plants did not all receive the same treatment.
6

Does this procedure describe a completely randomized design for this experiment?

A
No, the subjects are asked to return in three days. It is possible that some may not return, which will introduce bias into the results.
B
Yes, the subjects are receiving either the new cream or the inactive cream.
C
Yes, the subjects will all be exposed to poison ivy and then apply the cream.
D
Yes, the subjects are assigned to the two treatment groups completely by chance.
7

Which of the following describes a randomized block design?

A
The subjects are grouped based on their outdoor activity. The 42 subjects are randomly assigned to the two treatment groups. The remaining 58 subjects are also randomly assigned to the two treatment groups.
B
The subjects are paired based on similar age. Two marbles, one red and one blue, are placed in a bag and mixed. If the first subject picks a red marble, then that subject will receive the new cream and the other subject will receive the inactive cream. If it is blue, then the opposite will occur. This is done for all 50 pairs.
C
The subjects are numbered 1–100, and these numbers are entered into a random number generator. Fifty numbers, ignoring repeats, are generated and these subjects receive the new cream. The remaining 50 receive the inactive cream.
D
The subjects are grouped based on their outdoor activity. The researchers flip a coin and if it lands on heads, then the group with the most sun exposure will receive the new cream and the other group will receive the inactive cream. If the coin lands on tails, then the group with the most sun exposure will receive the inactive cream and the other group will receive the new cream.
8

Which variable would not be an appropriate variable for blocking?

A
breed
B
age
C
size
D
color of coat
9

Does this procedure describe a completely randomized design for this experiment?

A
Yes, the tires are randomly assigned to each vehicle.
B
No, the company did not use 20 of the same type of vehicle to receive both treatments, the new and original treads.
C
Yes, there are two treatments, new and original treads.
D
No, even though randomness is used, the procedure does not ensure that an equal number of vehicles are in both groups.
10

Which of the following describes a completely randomized design for this experiment?

A
The 50 subjects are paired based on running ability. The fastest two runners are paired together, the next fastest, etc. For each pair of runners, the researcher will flip a coin. If the coin lands on heads, the first runner will receive the new model and the second runner will receive the original model.
B
The subjects’ names are written on equal-sized slips of paper and placed into a hat. A researcher then reaches in and pulls out 25 slips of paper. These subjects are assigned to the new model group. The remaining 25 subjects will be assigned to the current model group.
C
The 50 subjects are grouped based on running ability. Twenty runners classify themselves as competitive runners and the remaining 30 classify themselves as recreational runners. For the competitive group, the runners’ names are written on equal-sized slips of paper and placed into a hat. The slips are shuffled, and the first 10 runners wear the new model and the other 10 wear the current model. The same procedure is used to assign the shoes to the recreational group.
D
The subjects are numbered 1–50 and these numbers are put into a random number generator. The first 25 random numbers, ignoring repeats, represent the subjects assigned to the new model group. The remaining 25 subjects will wear the current model.

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