Question

1.7 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

Only options a, b, and c fit the criteria of a completely randomized design as they involve the random assignment of subjects to treatment or control groups, which is crucial for a valid experiment. Options d and e do not mention random assignment.

Step-by-step explanation:

Experiments that use a completely randomized design are characterized by the random assignment of subjects to treatment groups, which is essential for controlling the effects of lurking variables and ensuring that group differences are due to the treatment rather than preexisting differences. Random assignment is a process where all participants have an equal chance of being placed into any group, and it is critical for the validity of an experiment.

• a) This is an example of a completely randomized design because computers with different operating systems were randomly selected and then randomly assigned to receive either the new or existing software.
• b) This also uses a completely randomized design because the 50 fish were randomly divided between the two aquariums, with one receiving the treatment and the other not.
• c) The use of a computer to randomly assign participants to a supplement or placebo group is a hallmark of completely randomized design.

Options d and e did not mention the use of random assignment to create the treatment groups; therefore, they do not fit the criteria of a completely randomized design.