Double-blind studies?

Question

In double-blind studies, how is it possible to keep the researchers from knowing which group has received treatment and which group has received a placebo? I don't understand...

Answer 1

The researchers distribute the product out randomly and they don't look at which person gets which product and they don't write it down or anything.

Answer 2

The researchers prepare 2 batches to be administered. One is the real drug and one is a placebo. The vials, bottles, whatever are labelled with a code known only to the researchers

They then hand these over to the people who administer the solutions. They write down who was given what (code).

After a period the results are gathered - who got better, who didn't. Again, the researchers have no hand in this. The results are compiled.

Then they are handed back to the original researchers who initiated the test. They can tell by looking at the results (which have their code numbers on them) whether their experiment worked, failed or partially worked.

At no time does anyone involved in the testing know who got what or can even interpret the effectiveness of the experimental treatment until the original researchers get the results back. They have nothing whatsoever to do with the testing, besides preparing the samples and analysing the results.