A researcher tested a new drug designed to decrease depression.
She gave it to 100 clinically depressed patients and discovered
that their average level of depression, as measured by a
standardized depression inventory, declined after 4 months of
taking the drug. She concluded that the drug reduces depression.
What problem, if any, is there with this conclusion?
There is a problem, there study has low internal
validity.
There is a problem, this study is a correlation not an
experiment.
There is a problem, there is no control group.
There is no problem with the conclusion.