Answer:
They did not create a placebo control group
Explanation:
To get the correct result for the given experiment, the researcher should have taken the placebo control group. So, that he can foresee the effects of anti-anxiety drugs and placebo effect on the participants of the different group.
Placebo effect: In the psychology experiment, a placebo is a substance or treatment that has no side-effects. The experimenters may use a placebo control group (a group of subjects or participants who are confronted or exposed to the fake independent variable or placebo). The participants getting placebo treatment, will show improvement as well.