Blinded experiment facts for kids

Kids Encyclopedia Facts

A blind experiment is a special kind of experiment where some information is kept secret from the people involved. This secret information could influence how the experiment turns out. The goal is to make sure the results are fair and accurate.

Imagine you're testing a new video game. If you know which version is the "new" one, you might think it's better, even if it's not. Blinding helps stop these kinds of hidden influences. It reduces bias, which is when your expectations or beliefs unfairly change the results.

Blinding can be used for anyone in an experiment. This includes the people taking part, the scientists, the technicians, and even those who look at the data. Sometimes, it's hard or even impossible to blind an experiment. For example, if someone is getting physical therapy, they know they are getting treatment. A good plan for an experiment makes sure blinding is done as well as possible.

During an experiment, someone becomes unblinded if they figure out the secret information. For example, a patient might guess their treatment if they feel a certain side effect. Unblinding happens often, especially in studies about medicines. If someone becomes unblinded too early, it can make the experiment less accurate. Scientists are encouraged to check and report if unblinding happens. However, this is not often done.

Blinding is a very important tool in the scientific method. It is used in many areas of research. In fields like medicine, it is seen as essential. An experiment in medical research that is not blinded is called an open trial.

History of Blind Experiments
Why Blinding Matters
- Bias in Studies
- Understanding Blinding Terms
What is Unblinding?
Where Blinding is Used
See also

History of Blind Experiments

The first known blind experiment happened in France in 1784. A group called the French Royal Commission on Animal Magnetism did it. They were checking claims about "animal magnetism." This was a belief that a special fluid could flow between people.

The researchers blindfolded people who claimed to use this magnetism. They asked them to find objects that were supposedly filled with this "vital fluid." The people could not find the objects. This showed that the claims were likely not true.

In 1817, another early blind experiment compared violins. It checked the sound quality of a famous Stradivarius violin against a guitar-like one. A violinist played each instrument. A group of scientists and musicians listened from another room. This stopped them from being biased by seeing the instruments.

An early example of a double-blind study was in 1835. It was called the Nuremberg salt test. This test checked if very diluted homeopathic medicines worked.

Later, in the 1800s, a scientist named Claude Bernard suggested blinding researchers. He thought that the person watching an experiment should not know what hypothesis was being tested. This was a new idea at the time. Many people believed that only well-educated scientists could observe things correctly.

The first study with a blinded researcher was in 1907. It looked at the effects of caffeine. By the mid-1900s, it became widely accepted that researchers should be blinded.

Why Blinding Matters

Bias in Studies

When a study is not properly blinded, different types of bias can appear.

If patients know their treatment, their reports about how they feel can change.
If researchers are not blinded, they might observe things differently. This is called observer bias.
People analyzing data might favor results that match what they already believe. This is confirmation bias.

These biases usually happen without anyone meaning for them to. They can affect results even if people think they are being fair.

Understanding Blinding Terms

In medical research, you might hear terms like single-blind, double-blind, and triple-blind. These terms describe how many groups of people are kept unaware of certain information.

A single-blind study usually means the patients don't know their treatment.
A double-blind study means both patients and researchers don't know the treatments.
A triple-blind study means patients, researchers, and another group (like a safety committee) are all blinded.

However, what these terms mean can change from one study to another. Because of this, guidelines suggest not using these terms anymore. It's better to say exactly who was blinded to what information. It's also important to say how well the blinding worked.

What is Unblinding?

Unblinding happens when someone in a blinded experiment finds out information that was hidden from them. In medical studies, a patient might accidentally guess which treatment group they are in. If this happens before the experiment ends, it can cause bias.

Some unblinding is common in blinded experiments. Blinding is not always perfect. It's more like a scale, from no blinding at all to perfect blinding. Most studies fall somewhere in between.

Scientists try to check how well blinding worked. They might ask participants if they think they received the real drug or a placebo (a fake treatment). If the experiment was perfectly blinded, people's guesses should be random. If many people guess correctly, it means unblinding happened.

Unblinding After the Study

Post-study unblinding means revealing the hidden information after the study is completely finished. In medical studies, this tells participants which treatment they received. It's not required, but it's often done as a courtesy. Unblinding after the study is done does not cause bias. This is because all data has already been collected and analyzed.

Unblinding Too Early

Premature unblinding is when unblinding happens before the study ends. Unlike post-study unblinding, this does cause bias. There are rules for when someone can be unblinded early, usually only in emergencies. This process is always carefully recorded.

Premature unblinding can also happen if a participant figures out the hidden information. For example, if a treatment has strong side effects, people in that group might guess they got the real drug. In drug trials, scientists sometimes use an active placebo. This is a fake treatment that causes some side effects. This can help hide who got the real drug.

However, side effects are not the only cause of unblinding. Any noticeable difference between the treatment and control groups can lead to it. Sometimes, just asking people to guess what they received can make them try harder to figure it out. Also, some people in studies try to find information on social media. This can also lead to unblinding. Scientists recommend reporting all premature unblinding. But in reality, it is rarely reported.

Why Unblinding is a Problem

When blinding is not done well, it can make the experimental treatment look better than it is. This can lead to false positives. This means the study might show a difference when there isn't one.

It's often assumed that "blinded" experiments are truly blind. But without checking and reporting, we don't know if the blinding actually worked. Even a small error in blinding can make results look important, even if there's no real difference. This means many "significant" results in studies might be due to problems with blinding. Some researchers believe it should be mandatory to check how well blinding worked in all studies.

Where Blinding is Used

In Medicine

Blinding is considered very important in medicine. But it can be hard to do. For example, it's tough to compare surgery with non-surgical treatments in a blind way. Sometimes, a sham surgery (a fake surgery) might be used to help with blinding. A good plan for a study makes sure blinding is as effective as possible.

Studies show that unblinding happens a lot in drug trials. This affects both patients and doctors. This challenges the idea that blinding always works perfectly in drug studies. Unblinding has also been seen in other medical trials.

Pain Studies

A large review in 2018 looked at studies on chronic pain. Only a small number of these studies reported checking blinding. The review found that the overall quality of blinding was poor. It concluded that blinding was "not successful." Also, studies funded by drug companies and those with side effects were less likely to report on blinding.

Depression Studies

Studies have found a lot of unblinding in antidepressant trials. At least three-quarters of patients could correctly guess their treatment. Doctors also became unblinded. When patients and doctors are better blinded, the treatment effect seems smaller. This suggests that unblinding makes antidepressants look more effective than they are. Some researchers think antidepressants only work better than placebos because of these errors. They argue that antidepressants might just be active placebos.

Acupuncture Studies

It's debated if acupuncture trials can be truly blinded. However, a 2003 review found several ways to blind patients in acupuncture studies:

Using needles that just touch the skin.
Using acupuncture points not meant for the condition.
Putting needles outside real acupuncture points.
Using fake needles that don't go into the skin.

The review found no clear link between the type of fake treatment and the study results.

A 2018 study on acupuncture used needles that didn't go into the skin as a fake treatment. It found that 68% of patients and 83% of acupuncturists guessed their group correctly. The authors said the blinding failed. They hope that better fake treatments might allow for well-blinded acupuncture studies in the future.

In Physics

In physics, it's common to do blinded data analysis. This means scientists analyze data without knowing the final answer. After the analysis is done, they can "unblind" the data. Sometimes, they agree to publish the results no matter what they find. This helps prevent publication bias.

In Social Sciences

Research in social sciences can be very affected by observer bias. So, it's important to blind researchers in these fields. Sometimes, blind experiments would be helpful but are not practical or ethical. Blinded data analysis can reduce bias, but it's not often used in social science research.

In Forensics

In a police photo lineup, an officer shows photos to a witness. The witness tries to identify the person who committed a crime. The officer usually knows who the suspect is. This means they might accidentally influence the witness. There's a growing trend to use blind procedures. In these, the officer showing the photos doesn't know who the suspect is.

In Music

Blind auditions for symphony orchestras happen behind a curtain. This way, the judges cannot see the performer. Blinding judges to the gender of performers has led to more women being hired. Blind tests can also be used to compare the quality of musical instruments.