What Is A Single Blind Study? Single Blind vs Double Blind Studies

Clinical trials usually follow one of two models: single blind and double blind trials. We examine the differences and when each type is used.

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Written by Nazar Hembara, PhD

Published 20 December 2023

Clinical trials are an essential component of medical science, helping to discover new methods and treatments to help people manage their diseases and conditions, as well as finding potential cures.

They work by assessing human participants who are given experimental drugs and treatments to evaluate the effects, with monitoring conducted to ensure the safety of everyone involved. To guarantee the validity of the trial’s results, there are most commonly two types of trials used - a single or double blind study.

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What are blind studies?

Blind studies can sometimes be referred to as masked studies and involve the research of human participants in a clinical trial, with some of its critical aspects not disclosed to participants or researchers (or both) to avoid any bias. This improves the accuracy and reliability of the study’s results.

‘Blinding’ ensures greater objectivity and avoids any preconceived expectations, preferences, or beliefs from interfering with the study. This makes it possible to assess the effectiveness of medical treatment in the fairest way.

What are single blind studies?

In a single blind study, patients are not informed which study group they will be designated to, but the researchers will be aware. For example, they could be given either the experimental drug or a placebo.

This type of trial is designed so that the participant is not aware of what treatment is being studied, helping to avoid any bias that may influence the outcome of the clinical trial.

What are double blind studies?

A double blind study on the other hand is a trial where neither the participants nor the researchers know which study group each individual has been designated to. This helps to eliminate all bias, with some researchers perhaps having a certain level of loyalty to a drug being studied, or an invested interest in the medical intervention being approved.

This ensures more credible and valid clinical trials.

The key differences between single blind vs double blind studies

There are a number of key differences between a single and double blind trial that you should be aware of relating to the knowledge of the participant and the researchers.

In a single blind study, the participants are completely unaware whether they will receive a new, experimental drug or be given a placebo. However, the researchers and those administering the treatment will know which type of treatment is being given to each study group.

Meanwhile, in a double blind study, neither the participants nor researchers know what treatment is being given.

The benefits of single blind vs double blind studies

Both single blind and double blind studies offer unique advantages in scientific and clinical research.Their unique benefits is what makes them more or less applicable to certain types of studies.

Bias control and credibility

As the participants in single blind studies aren’t aware of the treatment they will be receiving, but are aware that the researchers know which group they have been assigned to and might see this as being unfair, especially if the study involves a group of participants receiving a placebo. This can have an impact on their expectations of the study, sometimes in a negative way. Some participants may feel they will receive no benefit from participating in the trial, which could result in them failing to complete the trial or affect the reliability of the outcomes they report.

In terms of researchers, their bias may come from an eagerness to see a medication approved by the FDA, or preferring a certain type of medical intervention over another.

In a double blind study, there is more control when it comes to avoiding bias, with both participants and researchers in the dark about what treatments are being assigned. This ensures the reporting of outcomes is more accurate based on the experience of the participant.

Objective data collection

In a single blind study, the data collection process can lose credibility due to potential bias, because the researcher has knowledge regarding each group assignment. This is why a double blind study is often preferred as it is more objective, as neither the participants nor researchers know what treatment has been issued.

Scientific validity

From a scientific perspective, there is a significant difference between single-blind and double-blind studies. In single-blind studies, where only the participants are unaware of the treatment they are receiving, the research can be susceptible to research bias. This bias can potentially affect the reliability and validity of the study's findings, as the researchers beliefs or expectations might inadvertently influence the study outcome

On the other hand, double-blind studies, where both the participants and the researcher are unaware of the treatment assignments, are generally considered to be more reliable and valid. This is because double-blind studies offer a higher level of control over biases, thereby providing more accurate and trustworthy results. By eliminating both participant and experimenter biases, double-blind studies ensure that the outcomes are solely a result of the intervention, making them the preferred method in many scientific research and clinical trials.


The more logistically complex a trial is, the more expensive it becomes as it requires additional time and resources to ensure the success of the study.

The cost-effectiveness of single blind studies is one of the key benefits compared to a double blind study. This is because blinding key aspects of a clinical trial from both participants and researchers requires more administrative resources.


Single blind studies are often more practical when compared to their double blind counterparts. This is because double blind trials can sometimes make it difficult for researchers and administrators to manage the trial effectively, especially for complex trials that involve a large number of participants.

Furthermore, ensuring the study remains blinded for its full duration can also provide a challenge when a large number of individuals are involved.

When a single blind study might be chosen vs a double blind study

Many factors can dictate when a trial sponsor chooses to conduct a single blind or double blind study, including the type of treatment that is being administered, expected bias, and also ethical considerations.

When is a single blind study used?

Single blind studies are often chosen because:

  • Resource constraints such as those limited by time, finances, and personnel could have an impact on why a single blind study will be chosen over a double blind.
  • The practicality and feasibility of a study can also influence the design of a trial, as blinding researchers and treatment administrators could create too many challenges in terms of the logistics of a clinical trial, making it infeasible.
  • Ethical considerations also need to be taken into account as a single-blinded trial may be deemed sufficient in regard to protecting the participant’s well-being and their rights, while a double-blinded trial may not.
  • There may also be certain behavioral and observational studies that do not require double-blinding. For example, this could be because the researcher's knowledge of the group assignment may have no impact on the accuracy and reliability of the data collected during the trial.

When is a double blind study used?

Double blind studies may be preferred because:

  • There may be a need to minimize bias as much as possible to ensure the results of the trial are deemed valid.
  • Any possible placebo effect may also need to be controlled to avoid bias which is made easier by double blinding.
  • When trialing a new drug or treatment, the safety and efficacy of the intervention need to be maintained to meet regulatory requirements. In many cases, a double blinded study is preferred by regulatory bodies to meet these needs.
  • For more complex medical interventions, there may be a series of studies conducted that assess a range of conditions and their outcomes. Double blinded trials can ensure fairer comparisons and result in more accurate evaluations of each intervention.
  • Double blinding helps to remove bias from data collection and analysis. This is especially the case in clinical trials where researchers play a pivotal role and may be invested in the success of the treatment being administered.

How to get involved in a single blind or double blind study

If you are interested in getting involved in a single blind or double blind clinical study then there are a range of avenues open to explore. Below are three options a person can consider to learn more about participating in a study.

Identify research opportunities by directly speaking to research institutions, universities, hospitals, and governmental health agencies and speak with them directly. Or you can contact clinical trial providers online to discuss the requirements of future trials.

Explore online databases and directories that specialize in listing clinical trials. These directories include ClinicalTrials.gov or the World Health Organization's International Clinical Trials Registry Platform.

Speak with your doctor, regular health provider, or a local clinic to discuss clinical trials that may be taking place in the near future. They may have knowledge of ongoing studies that you may be eligible for or can refer you to relevant research centers and institutions.


Choosing whether a clinical study will apply a single blind and double blind approach depends on a number of factors. These may include the type of clinical trial, the practicality of using single vs double blinding, ethical considerations, and the need to minimize any bias.

Although double blinded studies are typically the preferred option when designing a trial due to the degree of control they provide in terms of limiting bias, there are more challenges to overcome when compared to single blind studies. Single blind studies are often more cost-effective as they generally require fewer resources and can be much more practical.

This is why researchers and clinical trial sponsors carefully assess a range of factors when designing a trial, ensuring the results are as accurate as possible, while also maintaining a level of safety to meet regulations.

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