StatTutor Lesson - Matched Pairs and Other Block Designs

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StatTutor: Matched Pairs and Block Designs
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      Questions 1-3

      123

      Question 1.

      What is a block?

      		A.
      		B.
      		C.
      Incorrect. A block is a group of individuals that are similar with respect to some characteristic known before the experiment begins.
      Correct. A block is a group of individuals that are similar with respect to some characteristic known before the experiment begins.
      Incorrect. Try again.
      2

      Questions 4-5

      268

      Question 4.

      What are differences exhibited by these rats?

      		A.
      		B.
      		C.
      		D.
      Incorrect. These rats vary by size, breed and length.
      Correct. These rats vary by size, breed and length.
      Incorrect. Try again.
      2

      Questions 6-7

      323

      Question 6.

      Why is using litters as blocks a good idea here?

      		A.
      		B.
      		C.
      Incorrect. Whenever individuals are similar with respect to some characteristic and that characteristic is expected to affect the response, blocks should be used.
      Correct. Whenever individuals are similar with respect to some characteristic and that characteristic is expected to affect the response, blocks should be used.
      Incorrect. Try again.
      2

      Question 8

      371

      Question 8.

      How is control/comparison implemented in this experiment?

      		A.
      		B.
      		C.
      Incorrect. Control/comparison requires either a control versus an active treatment group OR two or more active treatment groups or both. In this experiment, five active treatments (five drugs) will be compared so it has comparison.
      Correct. Control/comparison requires either a control versus an active treatment group OR two or more active treatment groups or both. In this experiment, five active treatments (five drugs) will be compared so it has comparison.
      Incorrect. Try again.
      2

      Question 9

      376

      Question 9.

      What principle is fulfilled by randomly assigning rats to drugs within each litter?

      		A.
      		B.
      		C.
      Incorrect. Randomly assigning rats to drugs is what is meant by randomization in an experiment.
      Correct. Randomly assigning rats to drugs is what is meant by randomization in an experiment.
      Incorrect. Try again.
      2

      Questions 10-11

      384

      Question 10.

      Why is the randomization carried out within each litter?

      		A.
      		B.
      Incorrect. We recognize an experiment as being a randomized block design when the randomization is carried out within each group.
      Correct. We recognize an experiment as being a randomized block design when the randomization is carried out within each group.
      Incorrect. Try again.
      2

      Question 12

      396

      Question 12.

      Which principle is implemented differently for a randomized block design than for a completely randomized design?

      		A.
      		B.
      		C.
      Incorrect. In a randomized block design, randomization is carried out within each block whereas for a completely randomized design, randomization is carried out for all individuals available for the experiment.
      Correct. In a randomized block design, randomization is carried out within each block whereas for a completely randomized design, randomization is carried out for all individuals available for the experiment.
      Incorrect. Try again.
      2

      Question 13

      459

      Question 13.

      From the plots for the times to complete the maze for the five drugs, which drug had the fastest (lowest) times?

      		A.
      		B.
      		C.
      		D.
      		E.
      Incorrect. Since the blue plot is much lower than all of the other plots, those rats completed the maze in lower times.
      Correct. Since the blue plot is much lower than all of the other plots, those rats completed the maze in lower times.
      Incorrect. Try again.
      2

      Questions 14-18

      555

      Question 14.

      True or false: A matched pairs design is a special case of a randomized block design.

      		A.
      		B.
      Incorrect. This is a correct statement.
      Correct. This is a correct statement.
      Incorrect. Try again.
      2

      Questions 19-20

      598

      Question 19.

      For this example of matched pairs with twenty sets of identical twins, what type of pairing is used?

      		A.
      		B.
      Incorrect. Each set of identical twins is a pair of matched individuals.
      Correct. Each set of identical twins is a pair of matched individuals.
      Incorrect. Try again.
      2

      Questions 21-22

      659

      Question 21.

      Why is this experiment a matched pairs experiment?

      		A.
      		B.
      		C.
      Incorrect. In a matched pairs design, the blocks can be either paired individuals or paired measurements. In this experiment, each subject receives both treatments (colas), so the measurements are paired.
      Correct. In a matched pairs design, the blocks can be either paired individuals or paired measurements. In this experiment, each subject receives both treatments (colas), so the measurements are paired.
      Incorrect. Try again.
      2

      Question 23

      690

      Question 23.

      Do you agree with Coca-Cola's conclusion?

      		A.
      		B.
      Incorrect. With a completely randomized design, all individuals are randomly allocated to the treatment groups.
      Correct. With a completely randomized design, all individuals are randomly allocated to the treatment groups.
      Incorrect. Try again.
      2

      Question 24

      737

      Question 24.

      How was randomization carried out for the completely randomized design?

      		A.
      		B.
      		C.
      Incorrect. With a completely randomized design, all individuals are randomly allocated to the treatment groups.
      Correct. With a completely randomized design, all individuals are randomly allocated to the treatment groups.
      Incorrect. Try again.
      2

      Question 25

      748

      Question 25.

      For this completely randomized design, do the groups appear similar with respect to potential for weight gain?

      		A.
      		B.
      Incorrect. The bigger rats will potentially gain more weight than the smaller rats.
      Correct. The bigger rats will potentially gain more weight than the smaller rats.
      Incorrect. Try again.
      2

      Question 26

      805

      Question 26.

      What is unique about this design as compared to any other possible completely randomized allocation of rats to diets?

      		A.
      		B.
      		C.
      Incorrect. One rat of each size could be in each diet group with several different random allocations. And you could get other completely randomized designs that have rats of different sizes in each diet group. But this is the only design that will randomly assign one rat from each litter to each diet group.
      Correct. One rat of each size could be in each diet group with several different random allocations. And you could get other completely randomized designs that have rats of different sizes in each diet group. But this is the only design that will randomly assign one rat from each litter to each diet group.
      Incorrect. Try again.
      2

      Questions 27-28

      886

      Question 27.

      When can a completely randomized design be performed?

      		A.
      		B.
      		C.
      Incorrect. We should only perform a completely randomized design when the individuals are similar with respect to variables that might affect the response variable.
      Correct. We should only perform a completely randomized design when the individuals are similar with respect to variables that might affect the response variable.
      Incorrect. Try again.
      2

      Question 29

      933

      Question 29.

      What is the biggest advantage of a randomized block design (RBD) compared to a completely randomized design (CRD)?

      		A.
      		B.
      		C.
      Incorrect. A randomized block design reduces chance variation by removing the variation associated with the blocking variable. This gives a more precise estimate of chance variation. One further note: lurking variables cannot be eliminated, only dealt with. And in a true randomized block design, there is no interaction between the blocking variable and the explanatory variable.
      Correct. A randomized block design reduces chance variation by removing the variation associated with the blocking variable. This gives a more precise estimate of chance variation. One further note: lurking variables cannot be eliminated, only dealt with. And in a true randomized block design, there is no interaction between the blocking variable and the explanatory variable.
      Incorrect. Try again.
      2