The purpose of a control group in a randomized controlled trial is to help reduce the likelihood that any benefits (and risks) identified during the process can be attributed to factors other than the drug itself.
The trial could use a placebo control - a dummy pill that looks exactly like the treatment, but lacks the active ingredient.
If there is no control - no reference or comparison group - any improvement in health or other outcome cannot be attributed to the drug or treatment.
There may be others factors about being in the clinical trial that could explain the results, and without comparing what happens in similar patients taking part under similar conditions - but not getting the new drug - there is no proper measurement of any health changes that may be observed.
This value of employing a control group is produced only if the trial is sufficiently large. It must have enough people taking part to ensure that chance differences and unusual cases do not have a large effect on the results.
A control group is typically made up of people who are matched for age, sex and ethnicity, along with any other factors that may influence the effect of a drug or treatment, such as weight, smoking status or comorbidities.
The control group may receive a placebo - a dummy treatment that looks exactly the same as the drug being tested, but that does not actually contain the active agent - or may receive standard treatment without the additional treatment under investigation.
In some cases, typically those investigating the benefits of an intervention in healthy individuals, the control group may receive no treatment and simply be made up of individuals similar to those receiving a supplement or therapy.
The quality of the control group is important, in terms of how well its participants match those of the active group. For example, randomization (explained above) helps to ensure that there is no bias influencing the selection of people into the control group.
Good quality clinical trials will publish baseline measurements for both the treatment and control arms of the trial, allowing for direct comparison.
Comparison with standard treatment
Many trials investigating new drugs or treatments for a disease are designed so that the control group receives an established (standard) treatment for that disease. The purpose of this type of control is to find out if there is any comparative benefit from the new drug versus the standard treatment. Even if the new drug does appear to have a beneficial effect, the established treatment may still be safer and more efficacious.
Comparative drug trials are important beyond the pharmaceutical development process as they can help guide decisions about allocation of healthcare resources.
For example, healthcare policymakers around the world are particularly interested in how a new drug fares against existing treatment options, taking into account cost-effectiveness, effects on quality of life, and other factors that add to the picture of overall benefit and cost to society, as well as to individuals.
Policy makers also have to account for the lack of diversity in clinical trials when making decisions about health care guidelines and funding. Historically, clinical trials have typically been carried out using white male patients, resulting in the approval of a range of drugs and interventions that have subsequently been seen to be less effective or riskier in a different demographic.
Research in non-human animals or a limited section of the population is, in most cases, insufficient to recommend widespread use of a drug or treatment for the general population. Indeed, the approval of some drugs based on animal research has led to significant harm to human health as non-human animals are generally a poor model for the human response to a drug or treatment.
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