The present answer is; “we do not”! Or, in some very few well-controlled cases we can we some probability get indications for an effect!
But, below I give some more of my own thinking based on my paradigm (see science tabs).
But first, even making it worse to understand, we can assume that placebo processes are working at different levels, biological, (cognitive and precognitive) psychological and social-cultural levels. We need also to realize that it concerns present as well as absence of processer that promote or prevent placebo processes, of probably most we at present do not even have an idea of. Promising position in our reasoning?
If we focus on Limbic (spatial code, see PPT 2 Dual code cross-talk between old and new brain: a psychophysiological interplay.ppt) systems based placebo can override the expressions of symptoms of actual dysfunctions but
(a) if the more biological parts is not changed by the placebo tools after a while then the main dysfunction´s expressions/activities are masked – with can have destructive effects while preventing treatments (if any),
(b) the can be influences at all levels, that is real effects on the psychophysiological dysfunctional complex/cluster,
(c) or there may be substantial biological changes but not observed while operational conditioning may prevent Limbic unconscious (reporting to conscious cognitive systems information while the physiological dysfunction constructive changes cannot override the operational conditioned Limbic memory cluster activities/processing –> see PPT 2 Dual code cross-talk between old and new brain a psychophysiological interplay.ppt)) or
(d) there may be no effect at all, but
(e) the latter may actually not be the case while complex dysfunctions need time to change at all levels – of some we might not yet know of or understand. Spontaneous recover is a just “word” (an not a well-defined concept) which may be a result of slow placebo-like changes to explain observations we do not really understand – but need a word for.
Having a word for something we (believe more or less well identified) observe may have great risks! Many diagnoses are names based an observations without any understanding! I think the reader knows many! But having a name may be misunderstood believing Bechterew´s disease is nowadays somewhat more understood as ankylosing spondylitis. There are many examples. But having a name can prevent clinicians from thinking out of the Spondylitis box.
Why do I write the above in a text on placebo? Simply while word (understood as) correct or not is amused to be able to promote placebo effects. This while at least I assume that most elated to placebo thinking refers to our old brain in general and Limbic (mammalian) brain in particular. This means that it is not the accuracy of the word but a certain word is understood by an individual´s Limbic/Spatial code, which is mostly processes not consciously.
Simplifying? Sorry, it is more, placebo is understood as processes mostly not subjected to being clearly understood/identified/… of constructive, restructuring, restoring dysfunctions! But we do have the very opposite – nocebo, probably working in quite the same not very well understood way.
Giving up .. but there is a way. A humbled careful way where my way is to use the “patient as an educated, reasonable competent resource and coworker in own rehab” and use the extended toolbox tailoring each individual, patient or not, in more convenient way a long with the hypothesis that more and more “out of little acorns grow huge oaks”, where each acorn is what we at present understand as constructive for the actual purpose. Given they can not be harmful! Why could the be constructive? While what we at present may regard as an placebo effect concerns processes that can be observed and understood as such a possibility must be sufficient fast! What happens when placebo effects take longer time than enabling it to be understood as such? Is spontaneous recovery slow placebo effects not visible as such improving a dysfunctional state/process/…
That is at least what I am working with and which will be published when I have some reasonable acceptable case illustrations. Traditional methodology is not yet useful but perhaps IBED, Individual Biopsychosocial Evidence based Documentation, a kind of single case design.
Bo von Scheele, 2019-11-10