Placebos alter self-knowledge but not the actual condition

" this paper analyzed hundreds of medical studies focusing on all types of conditions. Crucially, its authors didn't simply focus on studies that involved groups of patients receiving placebos, but on studies that involved a group of patients receiving placebo treatments and a group of patients receiving no treatment whatsoever, so that the impact on the two groups could be compared."

"In short, this paper suggests that placebo treatments don't affect people's physical state in any measurable way, though they can improve patients' perception of their own condition. That's an important distinction — it suggests that while placebos may improve patients' mindsets, the popular idea that placebos can trick people's bodies into spontaneously healing themselves may be nothing more than smoke and mirrors."

Interesting, though I'd always assumed the placebo effect had been measured precisely by comparing patients with and without placebo treatments. It's difficult to believe that this hasn't been done before.
http://www.clearerthinking.org/#!How-powerful-is-the-placebo-effect/c1toj/568bd3e70cf21f6856d88bb3