In a simple blind study, the project leader knows which drug I am taking. There is a good chance that the effect of the drug on me is triggered by the placebo effect. But why is my placebo effect alleviated if the project leader does not know what I am taking either?
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I assume it’s just to eliminate further possible factors that could throw off the results: Such as you somehow learning (or believing to have learned) about the nature of the drug through interaction with people who _do_ know – or even skewed interpretation of the results (such as your verbal feedback) by others
A placebo is a special kind of “fake” medicine that doesn’t have any medicine in it. Sometimes people will feel better after taking a placebo because they think it is real medicine, and this is called the placebo effect.
A double-blind trial is a special way of doing a study where neither the people taking the medicine nor the people giving the medicine know who is getting the real medicine and who is getting the placebo. This is to make sure that the people taking the medicine don’t know if they are getting the real thing or not, which can help to minimize the placebo effect.
The reason why this helps is because if the people taking the medicine don’t know if they are getting the real thing or not, they can’t “trick” their bodies into feeling better just because they think they are taking real medicine. This means that the study can better see if the medicine is really working or if it is just the placebo effect.
If the researcher knows whether you got the real stuff or the placebo, they can (either consciously or subconsciously) convey that information to the subject….thus removing the “blind”.
There are a number of non-verbal ways people communicate information: body language, posture, voice intonation, editorializing or word choice, etc.
That’s why double blind is considered the gold standard. The researcher can’t inadvertently tip off the subject, because they don’t know.
So in a modern clinical trial, the “project leader” is really the drug company. It doesn’t really matter (from a placebo response perspective) if they know who is on the drug or not because they don’t even know the names of the subjects. It is important for other reasons.
The importance of a double blind trial is that your *doctor* doesn’t know if you are on drug or not. The study doctor is going to be interviewing you about how you are doing – asking if your symptoms are getting better or not. If they know if you’re on the drug or not, it could bias the way they ask the questions which could bias how you answer.
For example, a doctor who knows you are on placebo might say “how are your symptoms? The same as last visit right?” A doctor who knows you are on drug might say “how are your symptoms? Are you feeling better?” People would tend to respond more positively to the latter.
In many trials, the doctor is actually assessing your symptoms. In depression studies the doctor might be “rating” your appearance and demeanor. If the doctor knows you are on drug or placebo this could impact their rating of you.
It doesn’t. The point is that both arms will experience the placebo effect. So if the treatment works better you know it’s not just the placebo effect. It lets you compare the arms against each other on similar footing.
As other posters said if the doctor knows if you’re receiving treatment or placebo they might accidently interact with one arm or the other differently.
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