As far as I know, pain is fundamentally a mental phenomenon: the only way to know if someone is in pain is to ask them or observe a voluntary change in their be

As far as I know, pain is fundamentally a mental phenomenon: the only way to know if someone is in pain is to ask them or observe a voluntary change in their behavior. Until this changes, the only evidence we can have that a proposed treatment reduces pain is via self-report. As far as we can tell, though, pain is a real problem that affects many people. We need to find effective treatments for it, and as much as I’d like to see more objective evidence of efficacy, I can’t think of what that evidence would actually be. Maybe we’ll eventually understand what’s going on well enough for a more objective test, but that’s not the case today. We need to make the best judgements we can on poor information as we also try to increase the quality of information we have to work with.