Updated: 20th April 2023

What is a double-blind study in clinical trials?

3 min read By Lizzi Bollinger

When conducting clinical research, double-blind studies are often the chosen experimental design to avoid bias and maximize research validity. A clinical research study, also known as a clinical trial, is an experiment or observation performed on human subjects with the goal of collecting data on the efficacy and safety of various new treatments.  

The “gold standard” design for clinical studies is the randomized, double-blind placebo-controlled trial. Let’s break down this type of study: 

Randomization is when subjects are divided into groups by chance. This is done to fairly compare treatment effects. Randomizing the groups means the makeup of participants will be similar and therefore the effects of the treatments they receive can be analyzed against one another.  

Blinding is when information regarding the treatment is withheld from participants of the study. A participant could include the doctor, subjects, technicians, and/or data analysts of the trial. A study can be designed single, double, or triple blind. A single-blind study is when the subjects are blinded but the doctors are aware of the treatment. A double-blind study is when neither the subjects nor the doctor knows which treatment the subjects are receiving. Triple blinding involves withholding information from the subjects, doctor, as well as data analysts.  

Once the groups are randomly divided into two groups, one group receives the treatment under investigation while the other group receives a placebo. A placebo is a treatment that appears to be real but is designed to have no benefit. When executing the experiment, it is important that both the treatment and placebo are administered the same way and look similar so that both the doctor and patient do not know which they are receiving.

Why blind and randomize a study?

The goal of conducting a study randomized and double-blind is to minimize the placebo effect and bias, in other words, factors that are not related to the treatment being tested.  

By blinding the doctor, it prevents them from treating the subjects differently or tipping them off to their treatment and prevents bias. Bias such as observer bias, when the observer sees what they expect to see not what is actually happening, and confirmation bias, when the observer looks for and uses the data to support their own ideas. 

Blinding the patients or subjects of the study helps avoid a placebo effect, or in other words, when the patient thinks they are receiving the new treatment, but they are not and the belief in the benefit of the treatment and expectation of feeling better is strong enough to heal the body rather than the characteristics of the placebo. 

If the experiment is not double-blind and does not control for bias and placebo effect, it could lead to false conclusions. By conducting a randomized double-blind placebo-controlled study, the conclusion will contain statistically relevant information for evaluating if a treatment is effective overall. 

At the end of the study, the experiment is un-blinded, and the subjects are told what treatment they were given. Although, in the case that a patient experiences health complications during the trial, the doctor can “unblind” the participant to find out which treatment they were receiving and in order to treat them appropriately. If this does occur, the subject will be removed from the study. 

Unfortunately, blinding is not possible in all clinical trials. This is especially the case when the method of drug delivery may not be able to be blinded. For example, physical therapy treatments are difficult to fake.  

How are double-blind experiments useful in clinical trials

Clinical trials are conducted to test new treatments. When possible, double-blind studies are preferred because it allows analysts to compare data between the test group and control group and trust that the results have not been affected by bias or a placebo effect. The comparison to the control group will show how effective the new treatment is at healing the illness compared to taking the placebo. The trial will also provide data on the effects of the treatment. Both positive and negative effects will be tracked.

Tools for conducting double-blind trials

To manage clinical studies, researchers will use digital tools to help facilitate randomized, blinded experiments. Software, like the EvidentIQ RTSM, provides automated, streamlined randomization and trial supply management. Tools like this can implement simple to complex randomization strategies as required by experimental design specifications. Patients are assigned code numbers and a treatment group. The doctor and patients only know the code number to avoid bias, hence allowing the study to be double-blind. The software allows the researcher to track the patient’s feedback and mark their progress via an electronic patient diary. In addition to tracking the patient group and code numbers, software can also manage the site inventories and shipping schedules. A web-based software can also provide real-time access to randomization, supply data, and reports from all the study’s various sites. To stay organized and to help with execution of a randomized double-blind clinical trial, be sure to choose an appropriate digital tool to reduce bias and increase the validity of the experiment. 

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