Question

lesson 4.7 hw
select the experiments that use a completely randomized design. (there could be more than one correct answer)
participants in a study to determine the effects of a new weight - loss 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.
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.
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.
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.
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.

Explanation:

To determine which experiments use a completely randomized design, we recall that a completely randomized design randomly assigns experimental units to treatment groups without any blocking (grouping by a confounding variable) or non - random assignment based on other factors.

1. First experiment:

• Participants are divided into groups based on age (blocking by age) and then randomly assigned treatments within each block. This is a randomized block design, not completely randomized.

1. Second experiment:

• A computer randomly assigns participants into a group receiving the supplement and a group receiving an inactive pill. There is no blocking, and the assignment is completely random. So this is a completely randomized design.

1. Third experiment:

• Plants are assigned to fertilizers based on their location (outer edge or middle of the garden), not random assignment. So this is not a completely randomized design.

1. Fourth experiment:

• 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. The assignment of fish to aquariums (treatment groups) is completely random. So this is a completely randomized design.

1. Fifth experiment:

• Computers are first grouped by operating system (blocking by operating system) and then randomly assigned treatments within each block. This is a randomized block design, not completely randomized.

Answer:

The experiments that use a completely randomized design are:

• 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.
• 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.