Randomised controlled trials (RCTs) are considered the gold standard for testing the effectiveness of new drugs, treatments, and medical devices. A crucial component of an RCT is the control group, which provides a benchmark for comparison with the intervention being tested. There are two main categories of control groups used in RCTs:
concurrent controls
external controls.
Concurrent controls involve participants who are enrolled in the study at the same time as the intervention group. They are typically recruited from the same population pool and randomly assigned to one of the study arms. Here are the different types of concurrent controls:
Placebo Control: Participants receive a placebo, which is an inactive substance or treatment designed to resemble the intervention but with no therapeutic effect. Placebo controls are particularly useful for blinding participants and researchers to the intervention assignment, reducing the influence of bias. For example, in a drug trial, a placebo might be a sugar pill that looks identical to the medication being tested.
No-Treatment Control: In some cases, a no-treatment control may be used, particularly for conditions where there is no standard treatment or where objective measurements are used to assess outcomes. This type of control is ethically appropriate only when withholding treatment is not considered harmful. For instance, a study on a new exercise program for weight loss might compare an exercise group to a no-treatment control group who do not participate in any exercise program.
Active-Treatment Control: An active-treatment control group receives a standard treatment or another intervention that is already established for the condition being studied. This type of control allows researchers to compare the effectiveness of the new intervention against the current best practice. For example, a trial on a new medication for diabetes might compare the new drug to an existing medication with proven effectiveness.
Dose-Comparison Control: This type of control is used in studies that evaluate different doses of the same intervention. Participants are randomly assigned to receive different doses of the intervention, allowing researchers to determine the optimal dosage for efficacy and safety.
External controls involve a comparison group that is not enrolled in the current study. Here's the most common type of external control:
Historical Control: A historical control group consists of data from previous studies on the same condition or intervention. While this type of control can be helpful for providing context, it is generally considered less reliable than concurrent controls because there may be differences in the participants, methods, or other factors between the current study and the historical study.
The choice of control group in an RCT depends on several factors, including the nature of the intervention being studied, the availability of existing treatments, and ethical considerations.