11. (a) Consider a study designed to investigate the following claim. A toothpaste with an active ingredient is effective in reducing
plaque buildup on teeth.
The following design is proposed for the study.
Obtain 170 volunteers from the population of people with plaque buildup on
their teeth. Randomly assign 90 of the volunteers to use the toothpaste with
an active ingredient each day. Assign the remaining 80 volunteers to use a
placebo each day. Observe the number of people who experienced a reduction
of plaque buildup in each group after six months.
Is this an observational study or an experiment? Explain.