Indicate whether the following study is an observational study or a controlled experiment
Patients with Alzheimer's disease are randomly divided into two groups. One group is given a new drug, and the other is given a placebo. After six months they are given a memory test to see
whether the new drug fights Alzheimer's better than a placebo.
Select the correct answer below
OA. This is a controlled experiment. The researchers randomly assigned patients to either a treatment or control group, and they gave the patients a test afterwards to identify the effect of t
new drug. This satisfies a key criterion of controlled experiments.
OB. This is an observational study. The number of treatment groups is not sufficiently large to control for all relevant factors aside from the effect of the new drug on memory, a key criterion
controlled experiments
OC. This is an observational study. The researchers did not give the patients a memory test beforehand to measure the baseline score on the memory test, which is a key criterion of
controlled experiments.
OD. This is a controlled experiment. The researchers controlled for all other factors prior to assigning patients to either the treatment or control group, and ensured that the new drug is
effective prior to its use. This satisfies two key criteria of controlled experiments.