There can be some utility in comparing over time. If the patient indicates a 9 before intervention, and a 5 afterwards, that means something's helping. The relative weight of a 9 versus someone else's 9 is irrelevant in this usage.
"The patient indicates" is still based on their completely subjective process of turning a mental state into a number. If they indicate a 9 before intervention, they did so by comparing the feeling of this this trauma to the fuzzy memory of breaking a bone as a child and the more recent but less painful memory of burning their finger in the kitchen a couple weeks ago. Then they sit and suffer from this trauma at approximately that same level of pain for the next 2 weeks, they'll have a new baseline to compare against.
It really sucks that we have no objective measure of pain; a tricorder that you could aim at someone and get a number back would be infinitely better than what we have now.
Not really because people have a terrible memory for pain. It can be worse afterward and still be a 5 (vs 9) just because they have got used to the pain.
