Question

Select all experiments that use a completely randomized design.

A) A computer scientist is testing new antivirus software on computers that were built in the last month. Ten computers with operating system A were randomly selected, and ten were chosen with operating system B. Five computers with each operating system were randomly assigned to be scanned with the new software, five to the existing software.


B) To test an epidermal treatment on fish in polluted stream water, 50 fish with epidermal abrasions from the same stream are randomly placed into two aquariums. One aquarium receives the epidermal treatment, and the other receives no treatment.


C) In a fertility study designed to test whether a new supplement helps individuals increase egg production, a computer randomly assigns participants into a group receiving the supplement and a group receiving an inactive pill.


D )Scientists assign the plants on the outer edge of a garden to an old fertilizer and plants in the middle of the garden to a new fertilizer. At the end of one month, the scientists randomly select four plants from each group to measure growth and determine the results of the study.


E) Participants in a study to determine the effects of a new hair-growth remedy are divided into groups based on age, and each subject in each group is randomly assigned to receive the new remedy, an existing remedy, or a placebo.

Answer 1

Experiments A, B, and C employ a completely randomized design because they involve random assignment of participants or items to different groups, ensuring equal chances of being in any treatment or control group.

Step-by-step explanation:

The question pertains to identifying which experiments use a completely randomized design. A completely randomized design is one where all participants are randomly assigned to either an experimental or a control group, ensuring that each participant has an equal chance of being in any group.

• Experiment A fits the completely randomized design as the computers with different operating systems are randomly assigned to scan with either the new software or the existing software.
• Experiment B utilizes random assignment by placing fish into two aquariums randomly for treatment or no treatment, making it a completely randomized design.
• Experiment C applies a completely randomized design by randomly assigning participants to receive either the supplement or an inactive pill.
• Experiment D does not use a completely randomized design as the plants are not randomly assigned but are instead allocated based on their position in the garden.
• Experiment E uses random assignment within age-based groups to different treatment options, hence it does involve some element of randomization.

Based on the given criteria, experiments A, B, and C use a completely randomized design.