There have been trials of placebos against placebos. That's how it has been established that more placebos are more effective than fewer and also how the shape

There have been trials of placebos against placebos. That's how it has been established that more placebos are more effective than fewer and also how the shape and colour of the tablets relates to their effectiveness. If you want some references on this, look up Bad Science by Ben Goldacre. It's a good read, btw.