An experiment will have both control groups or placebo groups and experimental groups. The control groups are resembles placebo i.e. in which independent variable is the difference with experimental group.
For example, comparison of population with a false treatment (placebo group) is with population who has disease & getting a medicament (experimental group) within a community. In the above false treatment, control groups do receive a dummy mediation with no “active drug component to treat disease”. If the symptoms of disease are eliminated in patient due to “not by a belief of specific treatment” but because of effectiveness of treatment”. This is known as placebo effect.
The scientist is going to measure the changes in dependent variable, which need to be measured from subjects involved in the experimental groups with the groups who are not involved (control group).
The disease symptom elimination is due to effectiveness of therapeutic molecules then it is referred as therapeutic relationship.
Thus, the options (a), (c) and (d) are incorrect.
If the symptoms of disease are eliminated in patient due to “not by a belief of specific treatment” but because of effectiveness of treatment”. This is known as placebo effect.
Therefore, the correct option is – b. placebo effect.