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Double-Blind Study - Definition & Examples

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Market research 04 12
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What is a Double-Blind Study?

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When experiment studies are conducted, they usually involve the use of a treatment group and a control group. The treatment group is the part of the sample that receives the treatment being tested while the control group receives a placebo or no treatment at all.

The control group and the treatment group are identical in nature, and share all the same characteristics, barring that the treatment group receives the treatment while the control group does not. In a double-blind study, researchers and participants are both kept unaware of which participants are a part of the treatment group and which are not. The knowledge of who is in which study group may unintentionally alter participant or researcher behaviour. A double-blind study can help avoid this, ensuring that any differences between the groups can be clearly attributed to the treatment. 

Types of Blinding

Double Blind Study2

There are three main types of blinding used in experimental research, and they are:

Unblinded

In unblinded studies, also known as open-label studies. All parties are aware of which treatment the participant receives.

Single Blinding

In single-blind studies, only the participant is unaware of which treatment they receive. This is done to avoid any potential behavioural changes that may be caused by participants having the knowledge of whether they’re in the control group or treatment group.

Double Blinding

In double-blind studies, also known as double-masked studies, participants and researchers are unaware of which treatment the participant receives. Sometimes when researchers are aware of which participants receive the treatment, they may unintentionally treat them differently than how they do the participants in the control group. Double-blinding is used to eliminate biases that could be caused due to potential differences in researcher behaviour.

Triple Blinding:

Triple blind studies involve the participants, researchers, and data analysts being unaware of which treatment the participant receives. Researchers may sometimes expect a certain outcome causing them to analyse the data collected differently to arrive at the outcome they initially expected. Triple blinding can help avoid this.

Example of Double Blinding in Research

A great example of double-blinding is clinical studies that are conducted to test new drugs. In these studies, random assignment is used to allocate patients into two groups: the treatment/experimental group (which receives the drug) and the control group (which receives an inactive substance that looks identical to the treatment but has no drug in it). Participants and researchers are kept unaware of which participants are allocated to the treatment group.

Then, the effects of the drug are measured by recording any new symptoms noticed in the patients. This prevents observation bias as doctors are unaware of which participants are in which group. 

Toward the end, the study is unblinded, and researchers and participants are made aware of who is in which group. The data is then analysed to establish whether or not the drug had effects that were not seen in the control group, but only in the experimental group. 

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The Importance of Double-Blinding

Double-blinding is pivotal in studies to minimise bias and maximise the internal validity of the results. Studies should blind participants to ensure that the knowledge of which group they’re in doesn’t affect their behaviour and create bias. Researchers must be blinded as well as knowing which participants are receiving the treatment can alter their behaviour toward them, inadvertently influencing participant behaviour in the process as well. This too would create bias. 

Unblinded studies often result in participants modifying their behaviour or researchers perceiving effects differently based on their expectations of the drug. Blinding is a useful tool to eliminate the potential of such biases being created. 

The Inability to use Blinding

There may be studies where the use of double-blinding and triple-blinding is not possible. This is especially true for studies where a placebo or fake treatment cannot be administered to a control group. For instance, some treatments performed by physiotherapists cannot be faked.

In cases where the use of double or triple-blinding is not possible, researchers can take the following measures to reduce bias within the study:

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Single-Blinding:

In cases where double or triple-blinding cannot be used, the researchers can use single-blinding and by keeping just the participants blinded.

Preregistration:

Preregistration refers to a study’s specification that of the hypothesis-generating (exploratory) research must be seperated from the hypothesis-testing (confirmatory) research. This will help prevent researchers from taking other measures of analysis to arrive at the answer they initially expected.

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