Even if a test shows that 99.999% of the people tested cannot distinguish between two audio samples it is still possible there are perceptible differences that can be heard if our focus is directed appropriately. So that would render double blind test inconclusive as well, no?
One can always argue based on the need for an infinite sample to cover all possible outcomes. One could easily argue the sun will not come up tomorrow and at some point will probably be correct.
Interesting choice of username. I should change mine to "StupiderthanU" just to be consistent. DBTs are not my day job but I'll throw out a couple of observations (from fallible memory). Consider the following IME/IMO.
Auditory memory is about 6 seconds IIRC (and there's my out) from ages-ago AES studies. Amir can probably cite references. Switching time in any sort of comparison test must be well below that to provide valid results. The idea is to listen for
differences, not that A or B (or X) is
better. Some claim differences can only be clear over extended listening tests; the evidence says the opposite because memory is fallible, plus our perception of the music is influenced by our mental and physical state. The latter is a big player in differences, of course -- e.g. "mood matters". What long-term listening does IMO is help provide additional examples and things to listen for. Many times when I thought I heard something better or just different, a return to the previous system showed it was there all along. Getting something different/new tends to heighten our focus as listeners. In effect, we train ourselves to be better listeners, so we can identify changes. The (a) catch with long-term testing is that we really need to go back to the original state whenever a difference is detected, and that can be very hard to do. Not only does it often take considerable time, but often is flat-out impossible because we've gotten rid of the previous component(s). Thus the need for short-term testing like DBT/ABX to ensure what we think we hear is really there.
In the primordial past I was actually able to do that. It proved conclusively for me that some differences in electronics do exist, but the vast majority went away in a DBT. The new things I found were there all along. It was rather humbling for someone respected for his hearing and being able to distinguish the granular structure of atomic and molecular alignment in cables (OK, the latter might be a stretch...) to discover most things (cables) sound the same after all.