I cant really think Why is it needed to use double blind study since I think single blind i.e. only patient blind must work.In double blind both Investigator and patient will not know about the drug and doctor will have to identify who is given what which would lengthen the process of trial and I think if investigator knows it shouldn’t affect the outcome of study

For example: If a research group is developing an Alzhimer’s drug and they are in clinical phase how would it affect the investigator if he knows that a patient is given placibo or a drug to cure Alzhimer’s.

Whats’s your point in this and if you think double blind are better and you provide some example.