Double blind
From RationalWiki
Double blind describes any decision process where all parties directly involved are not given crucial information in order to avoid biasing results. It is most commonly used in the scientific method where the experimenter (and subjects, where applicable) will not know which part of the experiment is the "control" and which is the "variable".
The essence of the idea is that both the observer and the subject are "blind" to what part of the test they are conducting, hence the "double" blind.
It can also refer to other decision making, such as in Peer reviewed journals, where double blind means that the reviewers will not know the author's names, and vice versa. In practice, due to people in a field knowing each other and each others' work, sometimes this "blindness" can be rather transparent.
The most persuasive type of medical study, the Randomized Controlled Trial (RCT) is usually double blind, however it is not always possible to blind someone to an intervention. For instance, if someone is studying chiropractic techniques for managing low back pain, it is difficult for the subject and the experimenter to be blinded regarding the treatment. Sometimes this bias is partially corrected in "cross-over" trials, in which half the subjects receive one intervention, and then "cross-over" to the other intervention. Where it is possible to administer a convincing "placebo", or "mock treatment", double-blind testing provides the most reliable results.
Few patent medicines have been subjected to double-blind studies, as the FDA does not require any proof of safety or efficacy, and few producers wish to submit their products to such scrutiny.
[edit] Purpose
Medicines undergo statistical tests because the apparent effectiveness or ineffectiveness of a drug in a single person could simply be random coincidence due to external factors, unrelated to the medicine, having an effect on that person's health. Apparent effectiveness can also be due to subjective biases of the patient or the doctor affecting their reporting of symptoms. People often feel better when they think they have been given medicine, even if they haven't.
The first problem is solved by testing on a large group of people, instead of just one person, and taking the average. The chance of a large number of people coincidentally showing the same response is much, much smaller. By also testing a similar group of people who didn't take the drug, you can compare the two groups and isolate the effects of the drug from what happens normally.
The second problem is solved by not letting either the doctors who assess the treatment, or the patients themselves, know whether they received the medicine or not. That way
[edit] Disadvantages
Despite the recent hype about double-blind studies, they are not a magic bullet. They have many significant flaws.
One problem is that statistical tests are open to fraud. Scientific theories must make logical sense in order to be true, and can thus be easily recognised by anyone as true or false. Statistical tests on the other hand have no such requirement, so it is possible for researchers to fabricate data without easily being caught.
Another problem is that statistical tests randomly give a false positive (an incorrect result saying it works) a fixed percentage of the time. Statistical tests usually accept as proven anything that has less than a 5% chance of happening at random. What that means is that if you test something that doesn't work, 5% of the time the test will incorrectly show that it does work.
That allows researchers to continually repeat the experiment until they get the false positive, and only publish that study.
Another problem is that it is extremely unethical to do medical experiments on humans without a good reason. A researcher must have a reasonable expectation that the drug could be beneficial, and evidence that it will not harm the test subjects. For that reason, a drug needs to have a scientific basis, and has to be tested on animals, before it can be trialled on people. Doing medical experiments without these things is officially listed as a war-crime in international law. It is thus unethical and illegal to do double-blind tests on alternative medicine.
