The reference does not exist?
Actually, it does exist. Did you look? It’s right here: http://www.painphysicianjournal.com/current/pdf?article=MTcwNA%3D%3D&journal=68
Now, having said that, the authors of this paper claim that there is no “under treatment of pain” happening in the United States, except millions of pain patients are not finding relief. So, I trust nothing published in this “journal” anyway.