A shoe company wants to test an updated model of a running shoe on its wear after one month of running. They recruit 50 people who run on a regular basis to participate in the study. Twenty-five runners will receive a pair of the new model and the remaining 25 will receive a pair of the current model. After one month, the wear on the shoes will be determined using the depth of the tread and the flexibility of the toe box. The wear between the new and current models will then be compared.

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

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.
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.
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.
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.