Blinding is a procedure in which one or more parties in a trial are kept unaware of which treatment arms participants have been assigned to, i.e. which treatment was received.
Blinding is an important aspect of any trial. How a trial was blinded should be accurately recorded in order to allow readers to interpret the results of a study. If blinding is ever broken during a trial on individual participants, it needs to be justified and explained
Why Do We Blind?
Blinding is used to prevent conscious or unconscious bias in the design of a clinical trial and how it is carried out. This is important because bias can affect recruitment and allocation, care, attitudes, assessments, etc.
It is used to ensure the objectivity of participants, study staff, clinicians, data collectors, outcome adjudicators and data analysts.
What Are The Potential Sources Of Bias in a Trial and Who Can And Should Be Blinded?
The relevance of blinding in a randomized clinical trial will vary according to circumstances.
The trial participant
Blinding participants to the treatment they have received is particularly important when the response criteria are subjective, such as alleviation of pain, but less important for objective criteria, such as disease progression (e.g. cancer). If participants are not blinded, knowledge of group assignment may affect their behaviour in the trial and their responses to subjective outcome measures.
For example, a participant who is aware that he is not receiving active treatment may be less likely to comply with the trial protocol. Those aware that they are receiving or not receiving therapy are more likely to provide biased assessments of the effectiveness of the intervention — most likely in opposite directions — than blinded participants.
Clinical staff administering treatment
Similarly, medical staff and clinicians caring for patients should be blinded to treatment allocation to minimise possible bias in patient management and in assessing disease status. Blinded clinicians are much less likely to transfer their attitudes to participants or to provide differential treatment to the active and control (placebo) groups than are unblinded clThe doctor assessing treatment
Blinding of data collectors and outcome adjudicators (sometimes the same individuals) is crucial to ensure unbiased ascertainment of outcomes. For example, in a randomised controlled trial in patients, neither active treatment regimen (tested medication vs. comparator) was superior to placebo when assessed by blinded specialists, but there was an apparent benefit of treatment with the test medication, when unblinded specialists performed the assessments.
1. Types of Blinding in Clinical
Research
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2. Blinding Blinding is a procedure in which one
or more parties in a trial are kept
unaware of which treatment arms
participants have been assigned to,
in other words, which treatment was
received
3. Types of Blinding ● Single Blinding
● Double Blinding
● Triple Blinding
● Open Blinding
4. Single Blinding If participants know whether they
were assigned to the treatment or
control group, they might modify
their behavior as a result, potentially
changing their eventual outcome.
In a single-blind experiment,
participants do not know which
group they have been placed in until
after the experiment has finished.
6. example
You have developed a new flu vaccine. In order to test the
effectiveness of your new treatment, you run an experiment,
giving half of your participants the flu vaccine and the other
half a fake vaccine that will have no effect (to control for the
placebo effect).
If participants in the control group realize they have received
a fake vaccine and are not protected against the flu, they
might modify their behavior in ways that lower their chances
of becoming sick – frequently washing their hands, avoiding
crowded areas, etc. This behavior could narrow the gap in
sickness rates between the control group and the treatment
group, thus making the vaccine seem less effective than it
really is.
To prevent such an outcome, in a single-blind study, you hide
from the participants which vaccine – real or fake – each of
7. Double Blinding
When the researchers administering the
experimental treatment are aware of each
participant’s group assignment, they may
inadvertently treat those in the control group
differently from those in the treatment group.
This could reveal to participants their group
assignment, or even directly influence the
outcome itself.
In double-blind experiments, the group
assignment is hidden from both the participant
and the person administering the experiment.
9. Example
In the flu vaccine study that you are running, you have
recruited several experimenters to administer your vaccine
and measure the outcomes of your participants.
If these experimenters knew which vaccines were real and
which were fake, they might accidentally reveal this
information to the participants, thus influencing their
behavior and indirectly the results.
They could even directly influence the results. For instance, if
experimenters expect the vaccine to result in lower levels of
flu symptoms, they might accidentally measure symptoms
incorrectly, thus making the vaccine appear more effective
than it really is.
To avoid this, you hide group assignments from both the
participants and the experimenters giving the vaccines – a
double-blind study.
10. Triple blinding Although rarely implemented, triple-blind
studies occur when group assignment is
hidden not only from participants and
administrators, but also from those tasked
with analyzing the data after the experiment
has concluded.
Researchers may expect a certain outcome
and analyze the data in different ways until
they arrive at the outcome they expected,
even if it is merely a result of chance.
12. Example In your vaccine study, you have also
recruited assistants to analyze the data you
gathered on flu infection rates. You decide to
hide the group assignments from the
participants, the people administering the
experiment, and the people analyzing the
data – a triple-blind study.
To achieve triple blinding, you assign each
participant to group 1 or group 2, but do not
inform the data analysts which number
represents which group.
14. Open Blinding Open Blinding is a procedure in
which parties in a trial are kept
aware of which treatment arms
participants have been assigned to,
in other words, which treatment was
received.
