Long article, but I think many on this forum would agree with the authors assertion that in most cases it doesn't make sense anymore to classify ED as purely "psycogenic" or "physical". I think we all experience that on a daily basis (especially us older guys). Some days stress levels are low, mood/confidence is high, therefore better erections. Or on the physical side, you aren't sleeping, eating like crap, T levels are low, erections suffer. It can be very hard to distinguish the two "causes" since they are so intertwined.
I think Peak would agree, but that seems to be one of the most asked questions here: "Is it physical or all in my head?". Most of the time, its both.