Efficacy studies refer to assessments of therapeutic effectiveness based on well-controlled investigation of well-defined clinical problems.
Efficacy studies is also defined as studies that place a premium on internal validity by controlling the types of clients in the study, by standardizing the treatments, and by randomly assigning patients to treatment or notreatment groups . A treatment is considered efficacious to the extent that the average person receiving the treatment in clinical trials is demonstrated to be significantly less dysfunctional than the average person not receiving any treatment, example, those on a waiting list for treatment.