Practice Test

Question 18 • Statistics

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

Answer

Number the plants 00–99 and, using a random number table, read the digits two at time. Select the first 50 digits. These will represent the plants placed in the fertilizer group. The remaining 50 plants will be placed in the group that does not receive fertilizer.

Number the plants 1–100 and put these numbers into a random number generator. The first 50 unique numbers generated will represent the plants placed in the fertilizer group. The remaining 50 plants will be placed in the group that does not receive fertilizer.

Group the plants based on size with the 50 biggest plants in one group and the 50 smallest plants in the other group. Flip a coin, and if it lands on heads, give the first group of 50 the fertilizer. If it lands on tails, give the second group of 50 the fertilizer.

For each plant, flip a coin. If the coin lands on heads, the plant will receive the fertilizer. If the coin lands on tails, the plant will not receive the fertilizer. Continue until 50 plants have been assigned to each of the two treatment groups.

Explanation

A completely randomized design assigns the treatments to individual plants using chance. In D, a random number generator selects 50 distinct plants from the 100 for fertilizer, and the rest form the no-fertilizer group. A could select the same plant more than once, while C assigns treatment based on plant size, so those are not suitable completely randomized designs.

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