Question

Killing weeds A biologist would like to determine which of two brands of weed killer is less likely to harm the plants in a garden at the university. Before spraying near the plants, the biologist decides to conduct an experiment using 24 individual plants. Which of the following two plans for randomly assigning the treatments should the biologist use? Why?

Plan A: Choose the $12$healthiest-looking plants.

Apply Brand X weed killer to all $12$of those plants.

Apply Brand Y weed killer to the remaining $12$plants.

Plan B: Choose $12$of the $24$plants at random. Apply

Brand X weed killer to those $12$plants and Brand Y

weed killer to the remaining $12$plants.

Short answer

Three experimental design:

• Lurking variables.
• Arbitrary assignment.
• Duplicate.

Step-by-step solution

Given Information

Experiment is based on which brand killer is less harmful for plants. Experiment on $24$plants are performed.

Plan A: Choose the $12$healthiest-looking plants.

Apply Brand X weed killer to all $12$of those plants.

Apply Brand Y weed killer to the remaining $12$plants.

Plan B: Choose $12$of the $24$plants at random. Apply

Brand X weed killer to those $12$plants and Brand Y

weed killer to the remaining $12$plants.

To determine experimental design principles

The principles of experimental design are:

• Outcomes of lurking variables control. Equate minimum two classes.
• Assign arbitrary subject to each category.
• Duplication is necessary

Plan A is not preferred as randomization is not used. Therefore plan B is preferred.