Experimental Designs — Quiz

Question 1 • Statistics and Probability

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

Answer

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.

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.

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.

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.

Explanation

A randomized block design first divides subjects into groups that share an important characteristic, then randomly assigns treatments within each group. Choice B groups runners by running ability and randomly assigns the shoe models separately within each group. Choice C pairs runners by ability and randomizes within each pair, which is a matched-pairs design.

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