Final answer:
The type of research study where treatment is tested on subjects, such as cell cultures, animals, or humans, and includes a control group is an intervention study. Notably, in placebo-controlled and double-blind intervention studies, control groups receive a placebo, and both researchers and participants are unaware of the group assignments to prevent bias and observe the true effects of the treatment.
Step-by-step explanation:
The research study type where treatment is tested on cell cultures, animals, or human participants is known as an intervention study. In these studies, participants receive specific interventions according to the research plan or protocol created by the investigators. These interventions may include medical products, such as drugs or devices; procedures; or changes to participants' behavior, such as diet. An essential feature of intervention studies is the use of control groups. A placebo-controlled study is one in which the control group receives a placebo, an inactive substance that has no therapeutic effect, to compare against the active treatment.
In double-blind studies, neither the participants nor the researchers know who is in the treatment or control group, which helps to prevent bias. This form of study is considered the gold standard for clinical trials as it helps to ensure that the effects observed are due to the treatment itself and not due to participants' or researchers' expectations, known as the placebo effect. An example of this would be a pharmaceutical company's clinical trial for a new drug to lower blood pressure that uses a control group receiving a placebo to observe the differences in outcomes and attribute them to the true effect of the drug.